Critical review of forensic trace evidence analysis and the need for a new approach.

Forensic Science International 251 (2015) 159–170

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Critical review of forensic trace evidence analysis and the need for a new approach David A. Stoney *, Paul L. Stoney Stoney Forensic, Inc., 14101-G Willard Road, Chantilly, VA 20151-2934, United States

A R T I C L E I N F O

A B S T R A C T

Article history: Received 12 November 2014 Received in revised form 17 March 2015 Accepted 23 March 2015 Available online 8 April 2015

The historical development, contributions and limitations of the two traditional approaches to trace evidence analysis are reviewed. The first approach was as generalist practitioner, looking broadly at an assemblage of many different particle types. The second was that of specialist practitioner, with attention focused on one specific particle type. Four factors have significantly impacted the effectiveness of these approaches: (1) increasing technological capabilities, (2) increasing complexity in the character of manufactured materials, (3) changes in forensic laboratory management, and (4) changing scientific and legal expectations. The effectiveness of each approach is assessed within the context of these changes. More recently, new technologies have been applied to some trace evidence problems, intended to address one or more limitations. This has led to a third approach founded on discrete, highly technical methods addressing specific analytical problems. After evaluating the contributions and limitations of this third approach, we consider the different ways that technologies could be developed to address unmet needs in forensic trace evidence analysis. The route toward effective use of new technologies is contrasted with how forensic science laboratories are currently choosing and employing them. The conclusion is that although new technologies are contributing, we are not on a path that will result in their most effective and appropriate use. A new approach is required. Based on an analysis of the contributions of each of the three exisiting approaches, seven characteristics of an effective trace evidence analysis capability were determined: (1) particle traces should be a major problem-solving tool, (2) there should be readily available, straightforward methods to enable their use, (3) all available and potentially useful particle types should be considered, (4) decisions to use them should be made in the context of each case, guided by what they can contribute to the case and how efficiently they can do so, (5) analyses should be conducted using appropriate technologies, (6) findings should be timely and directly integrated with case-specific problems, and (7) new technologies should be used to improve the overall effectiveness of the capability. Clearly new technologies have the potential to revolutionize forensic trace evidence, but just as clearly some of the traditional capabilities have been rendered ineffective, or lost entirely, by the way we have come to approach the problem. Having critically defined the current limitations of and the desired outcomes, the next focus should be consideration of alternative approaches that might achieve such a result. ß 2015 Elsevier Ireland Ltd. All rights reserved.

Keywords: Trace evidence Historical development Established methods Specialization New technologies

1. Introduction It is undisputable that forensic trace evidence analysis has undergone major changes since the times when analysis was confined to broadly trained general practitioners analyzing a wide range of traces using a light microscope. Some of these changes parallel those that have occurred generally within the forensic

* Corresponding author. Tel.: +1 703 362 5983. E-mail addresses: [email protected] (D.A. Stoney), [email protected] (P.L. Stoney). http://dx.doi.org/10.1016/j.forsciint.2015.03.022 0379-0738/ß 2015 Elsevier Ireland Ltd. All rights reserved.

sciences, others reflect the impact of changing priorities, and others reflect the impact of new technologies. A complex problem has emerged that is reflected in the diminishing use of trace evidence, reductions in funding and open debate regarding the viability of the discipline. This paper is offered as a critical review of the nature and causes of the problem, helping to define and understand objectives, but stopping short of considering possible alternative solutions. This is intentional. It is both confounding and confusing to hold the debate about a problem together with a debate about the solution; disagreements about one become interwoven with disagreements about the other. Solutions can be offered and debated based not on how they

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D.A. Stoney, P.L. Stoney / Forensic Science International 251 (2015) 159–170

address a well-defined problem, but rather because those offering the solutions view the problem differently. It is our strongly held view that to compare different solutions we must start with a common problem and, as such, this work is intended to provide the foundation for constructive consideration of alternative solutions (or indeed, a more focused debate on the problem). Forensic trace evidence analysis has traditionally been approached in one of two fundamentally different ways: as a generalist practitioner, looking broadly at an assemblage of many different particle types, or as a specialist practitioner, with attention focused on one specific particle type. This paper begins with descriptions of these two traditional approaches, their historical development and an analysis of their respective contributions and limitations. Over time, the significance and impact of the limitations has evolved in response to increasing technological capabilities in the laboratory, increasing complexity in the character of manufactured materials, changes in laboratory management and changing expectations in the scientific and legal communities. The effectiveness of each approach is assessed as it currently exists within the context of these changes. The more recent changes in technology have the potential to revolutionize trace evidence analysis. At the same time there has been an increased emphasis on scientific practices and standardization within forensic laboratories. These have had an impact on the traditional approaches and have led to a third approach, founded on component processes that employ new technologies. After evaluating the contributions and limitations of this third approach, we consider the different ways that technologies could be developed to address unmet needs in forensic trace evidence analysis. The route toward effective use of these new technologies is contrasted with the ways that forensic science laboratories are currently choosing and employing them. The conclusion is that although new technologies are contributing, we are not on a path that will result in their most effective and appropriate use. A new approach is required. The paper concludes with a summary of the hallmarks of an effective trace evidence capability and delineation of some key elements that we expect to be included in new approaches that attempt to address current limitations. 2. Traditional approaches to forensic trace evidence analysis Forensic scientists have long recognized the tremendous variety of particles that are ubiquitous in our environment. Hans Gross proclaimed that particle dusts are our ‘‘environment or surroundings in miniature’’ [1,2]. Edmond Locard echoed that they ‘‘may be formed of all the debris of all kinds of bodies. . . all the substances, organic or inorganic, existing on the earth’’ [3,4]. Heavily represented particle types on this list are minerals, plant and animal debris, microbes, industrial dusts, and fragments of manmade materials, but, as noted by De Forest [5] essentially anything can be encountered as crucial trace evidence in casework. This tremendous variety of particles occurs on items collected as evidence: clothing, bodies, and weapons – on virtually any object and within virtually any product. The particular combination of particles in or on an item is the result of a history of exposures and contacts, modified by the dynamics of adhesion and loss. As Locard noted, the particles are ‘‘the mute witnesses, sure and faithful, of all our movements and all our encounters’’ [3]. Particles are present and ready for analysis, in almost all casework [6]. The large numbers of adhering particles, as well as their variety, provide an extremely rich source of potential information, but they pose a correspondingly complex analytical problem. What is a reasonably efficient approach to the analysis and interpretation of many thousands of particles, occurring in many hundreds to thousands of different types? Two traditional approaches have

been developed to address this complexity. The first approach is that of a generalist, founded upon broad expertise and examination of many particle types. The second approach is one of data reduction, specializing in the detection and analysis of a very few particle types that occur prominently and frequently on evidentiary items. 2.1. First generation approach: generalist practitioners Microscopes began to be commonly used in legal cases in the second half of the19th century, leading to extensive application in forensic toxicology [7] and the detection of food adulteration [8]. The first applications of trace evidence analysis began in the same period and were closely associated with forensic medicine [9], focusing on the analysis of body fluids [10], feces [11], stomach contents [2] and hair [12]. More generalized applications developed in the casework of individual practitioners who used the microscope to identify and compare transferred particles [13]. Microscopic particle analysis was extremely effective, providing a broad range of information that contributed to the solution of a broad range of problems. Popular fiction romanticized these cases in the form of the boutique scientist, a renaissance man with broad expertise in the recognition and exploitation of minute traces [14–16]. The regular application to criminal investigation was conceptualized and encouraged by Gross [1,2], who strongly advocated engaging experts in microscopy. In the early 1900s case reports appeared frequently in the popular literature and in works on legal medicine. Summaries can be found in Locard [3,4,17,18] and elsewhere [19,20]. Notable case reports during the early 1900s included the work of Popp [20], Heinrich [21], Schneider [22–24], and Bertillon [25]. During the same period, an academic focus on criminalistics emerged in Europe [26–29]. Trace evidence was brought into the mainstream of criminal investigation through the development of dedicated police laboratories [28,30,31] and the publications and practices of Locard [3,4,17,18,27]. The early applications of microscopy to the analysis of trace evidence are striking in their multidisciplinary nature, yet they depended almost entirely on the application of the knowledge and skills of individual boutique practitioners. Three factors encouraged and enabled this capability. Firstly, expertise in analytical microscopy was much more common. Microscopes were a primary analytical tool used in chemistry [32–34], industry [35–40], pharmacy [41–43], geology [44–51], food analysis [42,43,52,53] and botany [54–58]. Secondly, a broad expertise in the microscopy of materials was reasonably achievable. Compared to later times, there was a much more restricted range and complexity of manmade materials to be encountered (textile fibers and paints are directly relevant examples). Thirdly, analysis with the microscope was state-of-the-art. Microscopical analysis, together with directly associated microchemical or microbiological methods, revealed all of the then-attainable character of the trace evidence. With this foundation of microscopy, and within the emerging crime laboratory structure, the 1930s and 1940s saw the development of trace evidence methods focusing on specific materials, notably glass fragments [59–65], paint [66,67], other building materials [68–71], hairs [72–76] and fibers [76– 79]. Microscopy, supplemented by increasingly sophisticated microchemistry [80,81] and a generalist approach [82] remained dominant into the 1950s and 1960s [83–87]. This approach ensured efficient, responsive application to individual cases. Any particle types encountered by an expert microanalyst were addressed by the methodology and their findings could be put immediately into the context of the individual case by the expert generalist practitioner. In this way the relevance of


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the examination to the case resolution was ensured. Questions of, ‘‘What is detected, why might it be present, and why should it be analyzed?’’ were inherent parts of the examination. During the second half of the 20th century the factors that had encouraged multidisciplinary analysis of trace evidence by individual boutique scientists were rapidly diminishing. Expertise in analytical microscopy became less common as college curricula changed [5,88,89] and chemical analysis in industry and pharmacy came more to rely on chromatography, spectroscopy and chemical instrumentation [90]. The range of materials encountered as trace evidence had also increased dramatically in the intervening years, challenging the feasibility and practicality of an individual maintaining appropriate competency and expertise. Furthermore, the skills in analytical microscopy that enabled this approach, although enduring as an essential component of trace evidence analysis [5,91,92], could no longer stand alone. They had not lost their relevancy, but they had lost their sufficiency. The analytical methods routinely used in crime laboratories expanded, adding significant capabilities [84,87,93,94]. Today, the expertise required for a generalist practitioner in trace evidence analysis is daunting. The materials that can be encountered are innumerable and the corresponding methods of analysis are complex. The education and experience required to achieve analytical proficiency and dependable, responsible interpretation has become enormous. Pasteur’s admonition that ‘‘chance favors only those minds which are prepared’’ [95] though often referred to in the context of trace evidence analysis [96,97] warns us that gaps in the individual’s expertise, widening with changes in manufacturing, product use and analytical methods will result in both missed and misinterpreted evidence.

experience) of whether the trace evidence material was common or rare. For example, some types of materials such as common soil minerals, or undyed cotton, were (appropriately) assessed of little or no significance because of their wide occurrence and their presence in most specimens [105]. Surveys of items representing the crime scene or suspect specimens, or accumulation of data from casework were means to provide a more definite foundation for these judgments. These studies began slowly, and were often motivated by efforts to determine the weight of evidence in a specific case. An early survey of glass fragments by Marris [59] is a good example. In the 1940s and 1950s, Kirk and colleagues studied the occurrence of colored wool fibers [78,106]. Beginning in the 1970s, coincident with population surveys of emerging serological markers, published studies of this type became common. Examples are: [107–111] for glass, [108,112] for paint, and [113–115] for fibers. Databases compiled from casework or comprehensive surveys, such as [116] for glass, also became available. Studies of the transfer and persistence of different trace evidence types such as [117–119] soon followed, together with a growing body of literature focused on how the new, quantitative data should be used in interpretive processes [99,120–127]. The continued expansion of analytical and interpretive methods, together with increasing complexity in the composition of materials, resulted in the specialization of trace evidence into sub-disciplines of hairs, fibers, paint, glass and soil [128]. The time had passed when it was credible to approach all particle types using a single instrument (the microscope) to demonstrate a correspondence between crime scene and suspect specimens, and to rely on a single expert’s experience to interpret the evidential weight of all types of traces.

2.2. Second generation approach: particle-type specialist practitioners

2.2.2. Particle-type focus and standardization of methods Specializations in the analysis of hairs, fibers, paint, and glass and have emerged as discrete disciplines within (particle-based) forensic trace evidence analysis [129]. These divisions are consistently used in the literature, certification programs, proficiency testing, professional societies and analytical symposia. Alternative groupings are encountered (such as a combination of architectural paints with glass and other building materials) based on laboratory organization, shared educational foundations, or similar analytical methodologies. Additional disciplines of gunshot residue analysis (GSR), explosives analysis and ‘‘general chemical unknowns’’ include particle analysis along with liquid phase analytes. Once the principal focus of trace evidence shifted to discrete particle-type disciplines, targeted methods of specimen recovery and analysis followed. Methods for efficient recovery and preliminary analysis of fibers, for example, are different from those that work efficiently for fragments of glass. Analytical methods necessary to achieve credible discrimination among paints are different than those that achieve discrimination among fibers, and so forth. Standardization of these methods was necessary for sharing of data among laboratories, and for determining frequencies of corresponding specimens in available databases. The importance of standardization increased with expanded expectations of specific measurables and explicit foundations for interpretations [130]. Implementation of particle-type specializations within forensic laboratories has had three important effects. Firstly, there has been a shift to categorization of examination requests and cases by trace evidence type. It is not unusual for specific types of trace evidence to suggest themselves by case circumstances. (Typical examples are hair found in a victim’s hand, the breaking of glass during a burglary, soil on a shovel used for burial, or paint flakes on a tool used for forced entry.) Secondly, there has been compartmentalization of laboratory activities, including the analyses themselves and the attendant

2.2.1. The compelling pressure toward specialization As the complexity of trace evidence analysis increased, a second approach emerged. This was one of data reduction–specializing in the detection and analysis of only a very few particle types that were recognized to occur prominently and frequently on evidentiary items. Specialization is a common response in many professions when there is a significant expansion in applicable scientific knowledge. Two major sources of this expansion affecting forensic trace evidence analysis in the mid-20th century have already been noted: rapid changes in how laboratory analyses were conducted and rapid changes in the range and complexity of the materials being analyzed. Initially, these brought two alternatives for specialization. Practitioners and laboratories with a generalized focus on particles [98] could adopt specializations based on instrumentation, while others could adopt specializations based on the different particle types [94]. In the 1970s, however, a third source of rapidly expanding knowledge also favored specialization by particle types: a growing body of research on the interpretation of trace evidence. Prior to the 1970s there was little systematic research on either (1) how often different types of trace evidence (e.g. fibers, glass, paint) were encountered on items of evidence or (2) relative frequencies of specific varieties of these particles (e.g. blue cotton fibers vs. red rayon fibers). Quantitative data of this type (whether definitively determinable or not) are directly relevant to the interpretation of trace evidence [99–104]. When laboratory analysis finds a correspondence between crime scene and suspect specimens, questions of evidential weight immediately follow. For a very long time these questions were addressed by statements that the specimens could have shared a common origin, together with an expert’s assessment (based on

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management processes. Laboratory personnel perform (and are only trained and approved to perform) more standardized, modular tasks. Expertise can become very narrowly defined – confined to the application of an explicit set of protocols. For example, one of our colleagues is currently trained and qualified to conduct examination and identification of general chemical unknowns in his laboratory. However, if his identification results in a finding of a particle of glass, he is no longer qualified, and the evidence must be transferred to another analyst. Likewise, if the particle is found to be a drug substance, a paint chip, or a fiber, these must be separated and transferred to appropriately qualified analysts within the laboratory. As another example, in one recent case pieces of tape were examined in five separate areas of a laboratory: hairs and fibers (for removal and analysis of adhering hairs and fibers), chemistry (for analysis of the tape adhesive and backing), trace evidence (for examination of fabric reinforcements in the tape); mineralogy (for examination of fiberglass reinforcements in the tape), and questioned documents (for physical fit of paper adhering to the tape). In such ways the particle specialist approach provides standardized results and interpretations, which address narrowly defined issues within narrowly defined case circumstances. Thirdly, there has emerged a discrete choice of which (now particle-type specific) services are to be offered by the laboratory. There are identifiable costs and commitments associated with acquisition and maintenance of analytical instrumentation, corresponding personnel, and the directly associated processes of training, certification and accreditation. Should the laboratory support hair cases? Glass cases? Soil cases? Which of these provide the most services to the laboratory’s constituency and help with legal decision-making in the most cases? 2.3. Evaluation of the effectiveness of established forensic trace evidence analysis methods It is instructive to evaluate and contrast the effectiveness of the two established approaches to trace evidence analysis: the first generation generalist and the second generation particle-type specialist. Each has its own contributions and limitations. The approach of the first generation generalist practitioner developed over a long time with a small set of expert-dependent tools. These tools could be chosen, applied and credibly controlled by an expert ‘‘machinist,’’ in response to the needs of individual cases. The quality was dependent on, but achievable by, an expert who could study a variety of commonly occurring particle types and address related interpretational issues. Unusual particle types, when present and relevant, could also be exploited, contingent on the range of the generalist practitioner’s expertise. When the level of science required for credible analysis was lower, and when the courts and society were more tolerant of personal experience as a foundation for opinions, the general practitioner approach was an effective solution to forensic trace evidence analysis. The quality and coverage of this approach, though still employed, has been stressed by the expansion of particle types, their increased compositional complexity and associated requirements of improved analytical methods and interpretive skills. As summarized in Table 1, the contributions of the generalist practitioner approach are (1) a wide variety of particle types can be recognized and exploited for their potential as trace evidence, (2) their analysis provides a broad range of information that contributes to the solution of a broad range of problems, (3) effective case solutions can occur when the particle types, expertise and problem to be solved coincide, (4) the methods employed are relatively inexpensive and easy to set up, and (5) the technology can be directly integrated with case-specific problems

Table 1 Contributions and limitations of the first generation generalist practitioner approach to forensic trace evidence analysis. Contributions A wide variety of particle types can be recognized and exploited for their potential as trace evidence The analysis provides a broad range of information that contributes to the solution of a broad range of problems Effective case solutions can occur when particle types, expertise and problem to be solved coincide The methods employed are relatively inexpensive and easy to set up The technology can be directly integrated with case-specific problems by the cross-disciplinary expert ‘‘machinist,’’ ensuring practical application to the problem Limitations An extraordinarily high level of individual expertise must be acquired and maintained Coverage is limited to particle types that overlap this expertise Technological developments continue to decrease this overlap There are increased probabilities of missed or misinterpreted evidence Increased legal and scientific expectations favoring standardization and compartmentalization are not met

by the cross-disciplinary expert ‘‘machinist,’’ ensuring practical application to the problem. The major limitations of this approach are (1) required maintenance of an extraordinarily high level of individual expertise, (2) coverage limited to particle types that overlap this expertise, (3) technological developments continuing to decrease this overlap, (4) increasing probabilities of missed or misinterpreted evidence, and (5) variance with legal and scientific expectations favoring standardization and compartmentalization. For second generation particle-type specialist practitioners, analytical and interpretive methods are focused on a small group of specific, pre-defined particle types. This has allowed development of targeted recovery methods, analytical methods with increased discrimination, standardization of methodologies, and development of databases useful for interpretation. In laboratories this has resulted in differentiation of cases by trace evidence type; increased costs for analytical instrumentation and staffing; more modular, technician-level tasks; less direct integration of laboratory work; and discrete decisions regarding which capabilities to offer. These changes have severely restricted the range of particle types that are considered for analysis, which (in turn) severely limits both the range of problems that can be addressed and the possible contributions that can result. As summarized in Table 2, the contributions of the particle-type specialist practitioner approach are (1) well-defined, predictable

Table 2 Contributions and limitations of the second generation particle-type specialist practitioner approach to forensic trace evidence analysis. Contributions There are well-defined, predictable tasks More highly discriminating tools can be applied Recurring, pre-defined problems can be efficiently addressed Standardization of analytical methodologies, protocols, training, and quality management can be achieved Interpretational tools based on this standardization can be developed Increasing legal and scientific expectations can be met Limitations A severely restricted range of problems that can be addressed and possible contributions that can result It is not adaptable or responsive to new problems Most of the particles available as trace evidence are unexploited. Specialized tools and niche expertise are required Methods and expertise can become very narrowly defined There is no longer a cross-disciplinary ‘‘machinist’’ as an effective integrator of the technology with the practical application to the problem


tasks, (2) more highly discriminating tools, (3) efficient solutions for recurring, pre-defined problems, (4) standardization of analytical methodologies, protocols, training, and quality management, (5) interpretational tools based on this standardization, and (6) meeting of increased legal and scientific expectations. The major limitations of this approach are (1) a severely restricted range of problems that can be addressed and possible contributions that can result, (2) it is not adaptable or responsive to new problems, (3) most of the particles available as trace evidence are unexploited, (4) specialized tools and niche expertise are required, (5) methods and expertise can become very narrowly defined, and (6) there is no longer a cross-disciplinary ‘‘machinist’’ as an effective integrator of the technology with the practical application to the problem. The limitations restricting the effectiveness of the two prevailing approaches to trace evidence work are the primary motivations for the writing this paper and define an opportunity for fundamental advancement. Would not it be nice if one could incorporate, rather than extinguish, the skills developed in the first generation and merge these with the technology developed in the second? 3. Current practices: recent changes and their impact This section describes recent changes in the use of technology, their effect on the traditional approaches to trace evidence analysis, and the emergence of a third approach based on component processes. 3.1. New technological advances and their potential contributions Advances in analytical chemistry and information technology have tremendously increased our capabilities in materials analysis. The range of materials that can be unambiguously identified and comprehensively characterized is extraordinary, and there is unprecedented sensitivity, specificity, and efficiency. These developments have much to offer forensic science. Which tools should we use and how should we use them? There are four major contributions that new technological advances can provide: (1) greater specificity and discrimination, (2) greater reliability, (3) broader application, and (4) greater efficiency. Greater specificity and discrimination are the result of more analytical information from the specimen itself and from a more comprehensive and relevant body of reference data. Examples are the use of LA-ICP-MS in the analysis of glass [131] and the use of Raman microspectroscopy in the analysis of paint [132]. Greater reliability results from methods that have less of a dependency on the contingencies of hands-on examination steps and observer subjectivity. These often accompany methods that minimize sample preparation, are semi-automated, and that provide objective, measurable analytical results. An example of minimization of sample preparation is the use of surface enhanced Raman spectroscopy for in situ analysis of fiber colorants [133]. Robotic methods of DNA analysis [134] are an example of semi-automated processing. Examples of objective, measurable results replacing subjective comparisons are the use of microspectrophotometry and multivariate statistical analysis for the measurement and comparison of dyed hair color [135,136] and similar methods applied to fiber dyes [137] and inks [138–140]. Broader application results when smaller specimen sizes can be accommodated or greater amounts of environmental alteration or dilution can be tolerated. Methods allowing micro-FTIR analysis or micro-Raman spectroscopy of individual particles [141] are good examples. Greater efficiency contributes directly to economy, but also increases the analytical throughput that allows more comprehensive collection of reference data that are needed for interpretation.

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Semi-automated particle analyses by SEM/EDS are a common example [142,143]. However, as we contemplate the potential contributions of new technologies, it is important to recognize that in a forensic context the advantages they offer are not intrinsically good. Whether or not increased specificity in the analysis (for example) represents an effective contribution necessarily depends on the particulars of the specific application, the impact on the full set of limitations, and the nature of any additional limitations that are introduced. Additional limitations from new technologies often include increased costs and restrictions on how broadly they can be applied (such as narrowly defined requirements on the types of specimens that can be accommodated). 3.2. Increased emphasis on scientific practices and standardization A combination of factors, beginning in the 1990s, resulted in greater scientific and legal scrutiny of forensic science practices. Apart from forensic specializations within established professions (such as forensic medicine and toxicology), the broader scientific community became interested in the forensic sciences with the advent of DNA-based identification methods [144,145]. During the same period, more intense interest within the legal community within the United States attended the redefinition of standards for the admissibility of scientific and technical evidence [146–148]. Subsequent evaluation of traditional forensic science practices, including re-examination of evidence in cases where DNA analysis resulted in reversals of conviction [149], has prompted debate [150], criticism [151] and fundamental scientific reviews [130,152–154]. All of these have brought renewed emphasis on scientific practices and standardization within forensic science disciplines. Trace evidence examination is no exception. Increased requisites for scientific practices and the increased attention of the scientific and legal communities are important changes promoting quality and reliability in the forensic science. Essential elements of all scientific practices include (1) a complete description of what was done, (2) documentation of analytical findings, and (3) a clearly articulated route from these findings to any conclusions that have been made. Standardized methods and objective measurements of known precision are two important means of achieving these elements. Standardized methodologies have well-defined input requirements and are designed to address well-defined problems with a known degree of specificity and reliability. 3.3. Impact of these changes on traditional approaches to forensic trace evidence analysis Technological advances and increased emphasis on scientific practices have reduced the effectiveness and viability of the trace evidence generalist practitioner. Access to new technologies is itself an obstacle. Additionally, fewer particle types are addressed, costs are increased, and the integration of technologies is more challenging. Two of the limitations in Table 1 coincide with the changes themselves: the continuing emergence of new technologies (increasing the education and experience required to achieve proficiency) and increasing legal and scientific expectations (favoring standardization and compartmentalization). For the particle-type specialist approach, the recent changes are well-aligned and directly intensify both the contributions and the limitations (Table 2). There is an added limitation of increasing costs. Whether or not there is a net improvement depends on the balance of the contributions and limitations in any specific context.

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4. A third approach: component processes 4.1. The allure of component processes Along with their impact on traditional approaches, the recent emphasis on scientific practices and standardization has resulted in a new approach based on component processes. This is another way to address the complexity of forensic particle analysis (as was the specialist’s focus on a small number of particle types). Component processes apply individual analytical methodologies to narrowly defined, isolated tasks. Examples are the use radionuclides for the classification of soil specimens [155,156], the use of GCMS for the discrimination of adhesive tapes [157], the use of ion chromatography–mass spectrometry for the analysis of explosives [158], the use laser-induced breakdown spectroscopy (LIBS) for the analysis of glass [159], and laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) for the analysis of glass and paint [131]. Component processes typically focus on greater precision and reproducibility of examinations, exploiting finer and finer compositional differences to push levels of discrimination toward the limits of within-source variation. These ultra-discriminating analyses can lead to interpretational difficulties since traces, once part of one single source, could be incorrectly ‘differentiated’ from the source due to the source heterogeneity if there is an incorrect assumption that the trace is representative of the source. Accordingly, there are greater requirements for the measurement of within-source variation and (when considering alternative sources) understanding the range of within-source variation within a relevant population. Despite these attendant interpretational difficulties, new technologies cater directly, and prominently, to those looking to the forensic science profession for adaptation of standard practices based on well-defined, modern scientific methods. There are other forces encouraging this approach as well. There is the general hope, pervading much of our society (and to which scientists are not immune) that new technologies will offer dramatic, plug-and-play improvements to long-standing problems. (Indeed, sometimes this can happen. For the forensic sciences, the emergence of DNA-based identification methods provides an explicit, inspiring example.) Further, the developers of new technology, researchers and funding agencies each have strong incentives to provide new applications. Finally, there is an inherent allure to these new technologies (we all like new gadgets) and strong marketing forces are in play to sell them, as a visit to in any trade show focused on forensic science or analytical chemistry will show. A more subtle force encouraging the component processes approach is that these processes are more easily understood. Compartmentalized problems can be unambiguously specified, without considering the broader context or overall effectiveness. Improvements or solutions to the compartmentalized problem can be conclusively demonstrated. For example, a need can be defined as one for more accurate and reproducible inorganic elemental analysis of glass. This need can be addressed conclusively by application of specific new technology. A clearly demonstrated improvement in this component process is much more easily understood than, for example, a problem of addressing the evidential weight resulting from the comparison of glass fragments with a putative source. In an increasingly complex world, as we face problems that are themselves inherently complex (such as the interpretation of trace evidence), a component process-based frame of mind can easily develop. 4.2. Evaluation of the effectiveness of the component processes approach The effectiveness of the component processes approach depends very much on the scale from which it is viewed. A local

view considers the contributions and limits of individual component processes as they perform their specific function. Do they reduce the input requirements and make an effective contribution to the local task, as defined? An expanded view considers the impact on the overall problem into which the component process fits. Are the overall input requirements reduced and is there an effective contribution to the overall problem? The evaluation of the effectiveness can be dramatically different. An example is where there is substantially increased efficiency in a task that is only of value in infrequently occurring circumstances, or that is linked to another task that is simultaneously made more complex. When a process has been determined to be a key component affecting the overall capability, improvement of the component can have clear advantages. Absent this determination, improvement in a component process is not intrinsically good (although a componentbased frame of mind can make it seem compellingly so). As summarized in Table 3, the contributions of the component processes approach are (1) well-defined, measurable improvements can be shown for specific tasks (such as greater specificity and discrimination, greater reliability, broader application and greater efficiency), (2) increased legal and scientific expectations favoring standardization and compartmentalization can be met, and (3) a range of particle types with similar analytical needs can be accommodated. The component-based frame of mind can also be susceptible to a number of phantom contributions that may appear to be inherently beneficial, but are not. These include (1) the perception that improvement in any component process represents an improvement in the capability, (2) the hope that new technologies can provide quick plug-and-play solutions, and (3) the hope that a specific new technology can become a universal solution to all problems. There are important limitations of the component processes approach: (1) severely restricted specimen input requirements, (2) infrequent applicability of any individual component process, (3) high costs for individual component processes, with prohibitively high collective costs for a suite of component processes, (4) fundamental interpretational limits, and (5) increased separation from the actual case-specific problems to be solved. 4.2.1. Severely restricted specimen input requirements Most advanced instrumental methods have narrowly defined inputs and outputs. That is, there is a specific question that is being Table 3 Contributions and Limitations of the component processes approach to forensic trace evidence analysis. Contributions There are well-defined, measurable improvements for specific tasks (such as greater specificity and discrimination, greater reliability, broader application and greater efficiency) Increased scientific and legal expectations favoring standardization and compartmentalization can be met Processes can be applied to a range of particle types with similar analytical needs Phantom contributions The perception that improvement in any component process represents an improvement in the capability The hope that new technologies can provide quick plug-and-play solutions The hope that a specific new technology can become a universal solution to all problems Limitations Severely restricted specimen input requirements Infrequent applicability of any individual component processes High costs for individual component processes, with prohibitively high collective costs for a suite of component processes Fundamental interpretational limits Increased separation from the actual case-specific problems to be solved


asked of a specimen, specific requirements for sample specimen preparation, and a specific form of data that follows. The analytical instrumentation is intentionally designed to perform in this way and it is not a disadvantage per se but an inherent limiting element. Problems in forensic science are non-standard and while advanced instrumental methods can contribute very effectively to solutions, they are not the kind of tool that is adaptable or widely applicable. By way of contrast, the microscopical methods of investigation that dominated first generation trace evidence analysis did not have this limitation. Microscopical analysis was inherently multifunctional, without narrowly defined inputs and outputs. 4.2.2. Infrequent applicability and high costs Although fitting well with the specialization of trace evidence by particle types, the instrumentation used for component processes must meet laboratory prioritizations based on the level of use and other factors such as: whether the instrument acquisition is essential to maintain core capabilities, whether multiple laboratory needs will be met, the impact that is likely on case resolutions, whether alternatives are available, and so forth. As previously discussed, the specialization of trace evidence by particle types reduces the range of cases to which a component process can contribute. The component process approach builds upon this specialization (without increasing the range of cases) and simultaneously increases the costs. The costs associated with new analytical technologies include those for the instrumentation itself, its maintenance and personnel costs (with allocations for specialized education, training and expertise). Given the narrow role that each component process plays in an overall capability, it is impractical to maintain the suite of instrumentation necessary to enable a broad capability (on anything short of the national level). 4.2.3. Fundamental interpretational limits The component processes approach also runs into fundamental limitations for the interpretation of trace evidence. Trace evidence can have a significant impact on case resolution, but as currently practiced this impact is almost entirely oblique to the level of technology that is applied. Existing methodologies provide a high degree of discrimination; specimens arising from dissimilar sources are efficiently distinguished. The additional discrimination that is provided by most new technologies is small. They sometimes serve as a cross-validation step, improving the reliability of associations, but they do not contribute significantly to the weight of the evidence itself. New technologies are generally applied to manufactured materials, including fibers, paints, glass, and tape. The composition of these materials is determined by their manufacture. As mass-produced commodities, there is a limit to the probative value that can be achieved by increasingly sensitive analyses. Fundamentally, the resulting associations are ones of classification: correspondence in properties that demonstrate a possible common source, among many others. Unresolvable difficulties of defining relevant populations and tracking the use of these commodities limit the significance of the finer variations in composition that would follow from increasingly discriminative methods [99,100,130]. Alternative, quantitative interpretive methods remain available through expert-dependent processes supported by more fundamental investigations and understanding of underlying causes of variability [160,161]. 4.2.4. Increased separation from actual case-specific problems Lastly, but very importantly, focusing on component processes leads the analysis further from the actual case-specific problems to be solved. Compared to either of the traditional approaches,

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component processes set more restrictive pre-conditions on what will be determined and how. Where is the means to efficiently integrate the increasingly specialized analyses?

5. Effective use of new technologies in forensic trace evidence analysis 5.1. Effective use of new technologies to realize contributions and minimize limitations There are many new technologies that have the potential to significantly impact trace evidence analysis and provide the contributions noted earlier: greater specificity and discrimination, greater reliability, broader application, and greater efficiency. The possibilities are exciting, but to achieve the contributions, associated limitations must be addressed. A fundamental tenet of the effective application of scientific methods to problem-solving is that capabilities are evaluated based on their input requirements and their effective contribution. Input requirements restrict the range of circumstances where the capability is applicable and the effective contribution is the improved problem-solving that results. Improvement must be judged in context, with respect to alternatives, costs and impact upon related processes. For example, an overall laboratory capability (such the use of trace evidence to address forensic questions of interest to the laboratory’s constituency) has a specific set of limitations on input requirements and effective contribution. Evaluation of the capability identifies these limitations and prioritizes them. Significant gaps or issues in the quality or effectiveness of the capability might be identified, such as low numbers of cases to which it is found applicable, high costs of analysis or low perception of probative value in those cases where it is applied. When a new component of a capability is considered (such as the use of a new SEM/EDX for the elemental analysis of particles, or a new method of interpretation, or a new method of reporting), this potential change is evaluated based on its impact; how does it affect the limitations on the overall inputs and outputs of the capability? Importantly, the changes may well address one limitation, while creating another. Or they may be a nice improvement of a component process, but not one that actually addresses a controlling limitation of the overall capability. (An example would be a quicker processing of specimens where this is not actually a rate limiting step.) A similar approach should guide which methods are chosen for the analysis of trace evidence in a specific case application. Inputs, required for the strategic use of any method, include case specifics, such as the questions of interest to the investigation, how the specimens relate to the case, and the specific nature of the specimens themselves. Understanding the specific nature of the specimens requires their preliminary analysis [5,82,162]. With this information as part of the input, determinations can be made of (1) the suitability for analysis by alternative methods (i.e. whether specimens meet their respective input requirements) and (2) the expected suitability of the output to meet the questions of interest in the case. With these inputs and projected outputs defined, the effectiveness of alternatives can be evaluated. Is it useful to characterize properties beyond general identification? Will broader compositional information be useful, or will there be value to more precise measurement of specific aspects? Are smaller fractions of the specimen feasible so that analyses can be repeated? Is it more valuable to investigate individual particles or the collective properties of a particle set? Can the rapid screening of many specimens allow an efficient, focused effort on a few that are representative?

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5.2. How new technologies are currently applied in forensic science Forensic laboratories are faced with a necessary balance of practical considerations surrounding the acquisition and implementation of new technologies. These considerations include applicability to cases, impact on case analysis time, staffing requirements, costs of acquisition, ongoing operational costs, and efforts associated with protocol development, quality management and laboratory accreditation. These factors create barriers to the implementation of new technologies, particularly if the technologies do not impact areas of the laboratory with existing high case volumes or with traditionally high probative value. As discussed in this paper, particle-type specializations have had the effects of (1) classification of cases by trace evidence type, (2) standardization of activities into modular, technician-level tasks, and (3) discrete choices of which (particle-type specific) services are to be offered. Laboratory accreditation and quality management activities also encourage (if not mandate) well-defined analytical protocols with directly related equipment maintenance, instrument calibration, training and proficiency testing. As a result, new technologies that are brought into forensic laboratories are intended to meet specific, targeted needs. For trace evidence applications, protocols for analysis of commonly occurring evidence types are well defined [129] and focus on achieving high levels of discrimination among traces from different sources. The modular application of instrumental methods for the specified applications is very effective. Infrared microspectroscopy of manmade fibers is a good example. Applied as a carefully selected tool, for a carefully selected purpose, standardized analysis determines the polymer combination that is present, allowing classification of generic type, queries of databases, and testing of association with possible sources. In this way, highly discriminating new technologies with specific applications have been incorporated into standardized methods of trace evidence analysis. These have replaced less discriminating, but more broadly applicable methods that depended on high levels of individual expertise. This change has been encouraged by growing legal expectations of greater standardization and reduced subjectivity. In summary, new technologies are incorporated into forensic laboratories (or sometimes in the field as with the current lab-ona-chip approach) when a well-defined, high-volume need has been established to justify their acquisition. Specialization of trace evidence analysis defines the context for these needs – standardized analyses on a small set of particle types that have been recognized to occur prominently and frequently on evidentiary items. Furthermore, growing emphasis on component processes has encouraged the use of new technologies to achieve greater specificity, discrimination and reliably in the analysis of a small number of particle types. Used in this way the costs of analysis are high and the numbers of applicable cases are reduced. Although the additional discrimination obtained by the new technologies does increase reliability, it does not address fundamental interpretational limits, and does not produce significantly more useful evidence. Overall, the laboratory costs to maintain the expertise and equipment necessary for trace evidence analysis are very high, a wide range of applicable technologies remain unavailable, and most particle types remain unexploited. 5.3. Looking forward: the impact of increasing technological capabilities on trace evidence analysis For the generalist practitioner, increasing technological capabilities will not improve the contributions and will continue to compound the limitations. The expert’s range of expertise becomes less relevant as the overall range in capabilities expands. That is,

the probability that the practitioner’s expertise will match the requirements of any specific case diminishes. Furthermore, as the gap widens between this expertise and prevailing practices, the probability of missed or misinterpreted evidence increases. New technological capabilities can be better assimilated by the particle-type specialist. Contributions are supported by addressing well-defined tasks with more highly discriminating tools. Often these are accompanied by increased efficiency and standardization. As applied, however, the new technologies intensify the limitations of the particle-type specialist approach. Expertise continues to narrow, methods are less adaptable, integration of technologies becomes more exigent, and most particle types remain unexploited. The component processes approach directly embraces new technologies, making demonstrable improvements for specific tasks and meeting increased scientific and legal expectations. At the same time the limitations of this approach, as currently applied, are extreme. Applications are constrained, the costs are exorbitant, fundamental interpretational limits are not addressed and there is wide separation from the actual case-specific problems to be solved. Technologies are improving and will continue to improve. They will continue to offer the potential capability improvements noted earlier; yet, following along any of these three approaches to trace evidence analysis, the result is predictable. There will be fewer cases where trace evidence is used, the costs will be high, and fundamental interpretational limits will not be addressed. The way that new technologies are being selected and used exacerbates the problems and impedes their solution. 6. Summary evaluation of approaches to forensic trace evidence analysis 6.1. Overall objectives of forensic trace evidence analysis As a form of evidence, particle traces should be a major problemsolving tool. Particle traces are always present and they have the potential to address a wide range of questions facing the forensic investigator. The route to the exploitation of these particles should be straightforward. Decisions to exploit them in casework should be guided by the knowledge of what they can contribute to the case and how efficiently they can do so, in the context of (and in concert with) other physical and investigative evidence. 6.2. Evaluation of the effectiveness of current approaches Particle traces have always been recognized as an important, highly informative source of physical evidence. The first generation generalist practitioner was effective in his day (when the level of science required for credible analysis was lower, and when the courts and society were more tolerant of personal experience as a foundation for opinions). This approach is no longer effective; the task is too complex to be managed within the limitations of the generalist approach. The second generation particle-type specialist approach deals with the complexities of particle analysis by discarding all but a few of the most obvious, larger, and more frequently occurring particle types. This solves complexity at the expense of practicality. Cases must fit narrow, pre-defined criteria, resulting in low numbers of applicable cases and higher costs to maintain the capability. The component processes approach shows intriguing potential for specific improvements, but (1) it clearly cannot operate as a stand-alone capability and (2) its impact on either of the other two approaches is to intensify their limitations. None of the current approaches meet the overall objectives for trace evidence analysis.


Many of the issues summarized in Tables 1–3 have been noted and discussed by others. The requirement of a generalist, multidisciplinary approach has been consistently emphasized for more than a hundred years. Period examples are Gross [1] (1894), Locard [3] (1930), Kirk [82] (1953), Kirk and Bradford [87] (1965), De Forest [5] (1982), Petraco and Deforest [163] (1993), Roux et al. [101] (2007) and Stoney et al. [19] (2013). As early as 1931 Schneider [22] emphasized the extraordinarily high level of individual expertise that was required for competent microanalysis. The close integration of results with case investigations has been consistently cited as an essential and largely unmet need [22,82,164–167], along with increasing difficulties maintaining this integration as centralized laboratories developed [168] and today as forensic science concentrates on issues such as ‘‘standardization, accreditation and de-contextualisation’’ [165]. Increasing specialization in trace evidence, followed by diminishing available resources and low case numbers, have resulted in explicit cancelation of trace evidence services [166]. Emphasizing the loss of resources during the 1990s due to a perceived low value relative to costs, Roux et al. [101] explored the ways that new technologies could improve the value of information resulting from trace evidence, or to reduce associated analysis times and costs. Key issues they identified were (1) the need to integrate forensic evidence with the investigative process, (2) the dysfunctional level of specialization within trace evidence analysis and the need for a return to the generalist approach, (3) the need for careful planning in the implementation of new technologies (evaluating their overall contribution and avoiding the allure of new technologies for their own sake), and (4) the need to recognize that discrimination is not the most significant feature for trace evidence analysis. The need for evaluation of capabilities based on the usefulness of the information that results, rather than on specific tools has been emphasized by Ribaux et al. [165]. The misguided reliance on component processes (or a ‘‘toolbox approach) as an ultimate solution has been discussed by Ribaux and colleagues [169], along with the effects of the relative isolation of forensic laboratories and perspectives driven by quality assurance. Overall, Robertson and Roux have argued that ‘‘serious coordinated action is required at an international level if trace evidence is to continue to meet the standards expected of forensic science in the future’’ [167]. Clearly there are complex and challenging problems facing the effective utilization of trace evidence in support of the forensic science mission. Some aspects of these problems are long standing, some are common to other areas of forensic science, and some are peculiar to the role of trace evidence. Most of the problems are exacerbated, rather than addressed, by the way that new technologies are being incorporated into laboratories and by the way that the profession has responded to pressures from the legal and broader scientific communities. A new approach is clearly necessary if we are to have an effective forensic trace evidence capability.

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(3) All available and potentially useful particle types should be considered. (4) Decisions to use them should be made in the context of each case, guided by what they can contribute to the case and how efficiently they can do so. (5) Analyses should be conducted using appropriate technologies. (6) Findings should be timely and directly integrated with casespecific problems. (7) New technologies should be used to improve the overall effectiveness of the capability. Secondly, within the complexities of the modern world, and in keeping with the requirements of good science and standardization, the capability would function similarly to the first generation generalist practitioner: exploiting all particle types, choosing appropriate technologies to do so, and directly integrating the findings with case-specific problems. Thirdly, the capability would take advantage of new technologies to improve the overall effectiveness of the capability. Naturally, the next focus is consideration of alternative approaches that might achieve such a result and our expectation is that the reader’s reaction, much like our own, is one of the anticipation for a well thought out solution. However, in our view the contribution of this review is as a carefully considered, critical definition of a major problem and we believe that it is important, explicitly, to offer any proposed solutions separately. There may be no practical solutions that retrieve the long past allure of exemplary cases solved by boutique scientists in the early 20th century. And yet there may be. In any event, as noted in the introduction, it is confounding and confusing to hold the debate about a problem together with a debate about the solution; disagreements about one become interwoven with disagreements about the other. Solutions can be offered and debated based not on how they address a well-defined problem, but rather because those offering the solutions view the problem differently. It is our strongly held view that to compare different solutions we must start with a common problem. Nonetheless, as we consider the range of possible approaches, we expect the key elements to include the following: Broad protocols that include preliminary examination of complex trace evidence mixtures, unrestricted by particle type, that allow for the recognition of traces of potential investigative or evidential significance. Quick protocols that will allow, at a more general level, informative, selective examinations that will help exclude sources or identify possible links using trace evidence. Readily accessible specialist resources that are practical to use and whose limitations, requirements and costs are both acceptable and well understood. Prompt integration of information and communication among investigators, trace evidence analysts and specialists, enabling timely, focused analytical requests and communication of findings.

6.3. Vision for an effective capability What would an effective trace evidence analysis capability look like? Firstly, it would address the overall objectives described in (A) above, becoming a major problem-solving tool that is routinely and regularly exploited to its full potential. Based on this review, the hallmarks of an effective capability would be: (1) Particle traces should be a major problem-solving tool. (2) There should be readily available, straightforward methods to enable their use.

Building such elements into a cohesive new approach will be challenging and alternatives should be considered in the context of the existing problem and the potential contributions. The underlying motivation for this review has been to provide this context and to encourage discussion of alternative new approaches. Acknowledgments This project was supported in part by Awards 2012-DN-BXK041 and 2010-DN-BX-K244 awarded by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice. The

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Illustration and analysis of a coordinated approach to an effective forensic trace evidence capability.

Thrombolysis: the need for a critical review.

Soil examination for a forensic trace evidence laboratory - Part 2: Elemental analysis.

Amblyopia: the need for a new approach?

Methylation Markers for the Identification of Body Fluids and Tissues from Forensic Trace Evidence.

Correction: Methylation Markers for the Identification of Body Fluids and Tissues from Forensic Trace Evidence.

A new anti-forensic scheme--hiding the single JPEG compression trace for digital image.

Liraglutide for weight management: a critical review of the evidence.

Suicidal or homicidal sharp force injuries? A review and critical analysis of the heterogeneity in the forensic literature.

The application of imaging technologies in the detection of trace evidence in forensic medical investigation.

Applying new evidence into practice: a need for knowledge translation.

Biosensors in forensic analysis. A review.

Translational research-the need of a new bioethics approach.

Dietary carbohydrate restriction as the first approach in diabetes management: critical review and evidence base.

Parricide: a forensic approach.

The Review of Nuclear Microscopy Techniques: An Approach for Nondestructive Trace Elemental Analysis and Mapping of Biological Materials.

Methodological problems in the use of factor analysis: a critical review of the experimental evidence for the anal character.

Critical care evidence--new directions.

Sinusitis: a critical need for further study.

Understanding the evolution of Mammalian brain structures; the need for a (new) cerebrotype approach.

Bisphosphonates and connexin 43: a critical review of evidence.

New evidence and critical reappraisal of available evidence: the task of a scientific journal.

Evaluation of the persistence of transformation products from ozonation of trace organic compounds - a critical review.

Detox diets for toxin elimination and weight management: a critical review of the evidence.