J. Forens. Sci. Soc. (1975), 15, 3
What can Science do for the Law? DAVID PATTERSON Department of Colour Chemistry, The University, Leeds, England
A Presidential Address delivered on the occasion of the Society's 15th Annual General Meeting in London on the evening of Friday, November 15, 1974. I n return for presiding in as impartial as possible a manner over the meetings of the Council of the Forensic Science Society, it was decided some three years ago that the President should be given the opportunity, in alternate years, of delivering to the Annual Meeting of the Society a Presidential Address. The first of these was duly given two years ago by my predecessor in this office, Dr. Julius Grant, and the subject he chose was Towards a New Profession? a title which he posed as a question. Now, one of the advantages of being an early speaker in such a series is that one is not restricted by the need to avoid topics that have been chosen by earlier Presidents. I have therefore selected the title also in the form of a question: What can Science do for the Law? This is indeed a very wide subject and I shall confine my remarks to a brief review of the period since the Society was formed in 1959, together with an attempt to look a little into the future. Both in my University employment, and as a magistrate, I am unused to consulting higher authority before expressing my opinions, since academic freedom and the independence of the judiciary are cornerstones of the pattern of British society. Neither can I claim to have consulted the Council of the Forensic Science Society as to what I should say, because I regard the independence of such scientific societies as ours, as of fundamental importance to the continuing health of Science and the development of our democracy, and this requires that there must always be on hand challenges to the existing orthodoxy in Science and in Government. For better or for worse then, what I am about to say is entirely a t my own responsibility. I n the opening address which I gave at the inaugural meeting of the Forensic Science Society a t the University of Nottingham in 1959 (Patterson, 1960), I attempted a definition of what constituted the main objects of forensic science, a t least as far as the criminal law is concerned. The essence of this was that what the Courts frequently wanted was a firm statement about the linkage between two objects. For example, did this fibre, paint chip, soil, wood, blood or whatever-something generally in small amount associated with a suspect, "the crime sample", come from a particular source known to be connected with a particular crime, "the control sample" ? Sometimes a definite answer can be given, but more often all that can be said is that the crime sample could have come from the control sample. I suggested that the number of examples where no clear answer could be given would be reduced by "refining methods so that smaller quantitative differences can be detected with certainty, and by the search for more subtle and unique links."
Sharpening the Tools Let us see what progress has been made since 1959 by a particular example. Suppose we are trying to see whether a bit of nylon filament found on a suspect's clothing came from a victim's garment. The first steps would be to establish that both were nylon of the same chemical structure (say Nylon 66 and not Nylon 6) ; that the denier and cross-sectional shape were the same (both circular). If the garment was dyed, then we would expect the crime filament to have the same colour under the microscope as control samples from the garment. This could all have been done in 1959, now we can go further.
I n the making of nylon itself a process called polymerization is used and to speed this up, substances called catalysts are added. These are metal salts of various kinds and their exact nature varies from manufacturer to manufacturer. Techniques are now available for identifying and measuring the amounts of these substances in single filaments. I n addition the transmission spectra of the single filaments can also be measured, removing an element of subjectivity from visual colour matching. Chromatography might also allow it to be said that the dyes used in garment and filament were identical, though here some partial interference with the crime sample would be necessary. The more properties that we can show are similar between crime and control samples, the greater the probability that the crime filament did come from the victim's garment. The process is similar to finding and increasing the number of points of similarity between crime and control fingerprints. I do not think that it will ever be possible to prove "beyond reasonable doubt" that a single filament came from a particular garment. But the more properties we can measure, the more we can eliminate other sources of the filament, pointing more and more definitely to the control source as being the true source or, on the other hand, of eliminating it, since as soon as any property is different, that source is eliminated. The value of the evidence of the identity of the two filaments is much higher if taken in conjunction with other non-scientific evidence. I t might be known for example that the shop had only sold six garments of the same type and colour in the town in question, and the other five could not possibly have been anywhere near the suspect. Such conjunction of scientific evidence and quite independently established facts can in my opinion build up a very strong case indeed against a suspect. I n practical terms, this means that the develoment of analytical methods for detecting increasingly specialized and increasingly minor constituents of fairly common materials, what I have termed "Sharpening the Tools" offers a powerful way in which Science can help the Law.
Some Difficulties Among the many new and powerful analytical tools introduced since the Forensic Science Society was founded, neutron activation analysis is one which perhaps best illustrates the difficulties which arise in the "sharpening the tools" approach. Many objects such as human hair contain minute quantities of metals which can be made radioactive by placing the object in an atomic pile. These tiny amounts can then be accurately measured. The presence of a number of these constituents in identical (though small) amounts seemed to be the ultimate in establishing the identity of origin of crime and control samples. But the method proved too sensitive. Variability of the analyses on samples along the length of a single hair and from place to place on an individual's head, still left difficulties in deciding that a single hair must have come from a particular head of hair. I n establishing the common source of specimens, then it is probably true that our tools are currently a little too sharp. Before we can exploit them, we need a much greater knowledge of the normal distribution of a large number of substances in our ordinary environment. Only then can we positively identify the abnormal as being outside this pattern. Fortunately, an increasing number of papers is appearing which provide this background information.
Scientific Offences I want to turn now to a second development in the field of forensic science which has occurred during the lifetime of the Society. It is the growth of the number of "scientific offences", by which I mean offences which are defined in terms of scientific measurements. Speeding in motor vehicles is the oldest and a new one is that of driving a motor vehicle with more than a prescribed amount of alcohol in the blood. Here there are fixed numerical thresholds for committing a n offence. I n built-up areas a speed of 29mph is unexceptionable, 3lmph means committing an offence. I n the blood, 79 milligrammes of alcohol per 100 millilitres of blood is blameless, 81mg alcoho1/100ml means loss of one's driving licence if one is caught. At least, so the law would have it, but everyone
knows in practice this is not so. Few prosecutions are brought for driving at speeds below 40mph or for blood alcohol contents below 95mg/100ml. Many years ago a colleague of mine sent a sample to a senior and respected analyst in a large chemical company. When he went to get the result he enquired what the error in the measurement was. The analyst was a Yorkshireman, he stuck his thumbs through his braces and with his feet on his desk retorted, "errors lad, we don't have errors, when ah gives tha a number that's it !" This is rubbish, of course, despite his eminence. There are well-known statistical laws governing the errors in repeat measurements of any quantity. The spread of values can be found by experiment, and the spread is characterized by the standard deviation. 95% of all measurements fall in a range of plus or minus twice the standard deviation. Thus if the true value were 8,O units and the standard deviation were 2 units, by this analytical method 95% of measurements would lie in the range 76-84 units; 99% lie in the range 74-86 units. What I have said applies to the errors in the actual analysis and there will be others which we will ignore for the moment. We are clearly not going to convict those who get an analytical answer below the legal limit, that is, those who whilst actually having 81 units, get results below this. What of those with a n actual amount of 80 units who get above 80? Justice clearly demands that no one should be convicted because of analytical errors. It has become customary for results to be reported as "not less than xmg alcoho1/100ml of blood", and as I said earlier 95mg seems to be the accepted level for prosecutions to be brought in courts where I sit. This allows such a margin for error that no one who is innocent should be convicted. We can expect the number and variety of scientific offences to increase. For one thing, such cases are very easy to decide; even the least numerate will not often be in error about deciding whether one figure is greater than another. I t is child's play compared with deciding whether a driver has exercised "due care and attention" when associated with a road accident. But there are more cogent reasons than this for expecting the number of scientific threshold offences to rise. I n an increasingly technological society we may expect many more regulations and laws concerning the permissible limits of chemicals in our environment-for example the quantities of colourants and additives in food, the amounts of sulphur dioxide in the air and the amounts of lead and carbon monoxide from vehicle exhausts. Then there is the futuristic offence of "Wilfully exposing the magnetic store of a computer to a field of x thousand gauss to the peril of the national records . . .". The proof of guilt in other offences may depend on the detection of small amounts of drugs and explosives. I n these instances we want to know the limits of detection of the materials in question by the analytical methods used, as opposed to the confidence limits on numerical results, since we can't go along with the eminent Yorkshire analyst and his touching but incorrect belief in accuracy. The second point I want to make, therefore, is that while Science can aid the law by defining offences in objective numerical terms, there should always be freely admitted and disclosed figures on the accuracy of the measurements involved in the securing of convictions for those offences.
No M o r e Cross-Examination Finally, I want to suggest something that the Law could do so that it may benefit fully from the assistance Science can givc it. I t concerns the treatment of scientific evidence in Courts. I am sure that what I have to suggest will have little immediate support from the legal profession. I n an accusatorial system of trial, cross-examination of witnesses is an essential part. Skill in it brings the highest reputations and rewards in the profession of the advocate. I t may well be the best method of wringing the truth from lying villains; I think it probably is, but I also think that the methods of cross-examination are quite inappropriate to the assessment of scientific evidence.
There will seldom be disputes between scientific experts on the results of scientific tests, not if the methods are exposed to the scrutiny of the widest scientific circles, as they should be. Even if there is, I still do not consider that cross-examination is appropriate. The most likely cause of dispute is the inference to be drawn from the results. I am not alone in my opinion that crossexamination is inappropriate in testing scientific evidence. Sir Roger Ormrod in a very perceptive article (Ormrod, 1968) said of cross-examination: "The questioner is dominant. The form of his questions conditions the form and often the content of the answers;" and later "Questions which contain hidden assumptions sometimes yield answers which almost contradict the witness's real meaning unless he is quick enough to detect and expose the assumption." There is obviously something seriously wrong when such a situation can occur. I n the same article, some possible solutions were propounded. One is the appointment of Court experts, possibly from an approved panel, to assist the Courts. Such a system appears to apply in California, since one of the stated aims of our sister society the California Association of Criminalists is to "Provide a board of review in cases involving differences of professional opinion when requested." Sir Roger's opinion is that such a system is unlikely to be acceptable in criminal cases in this country. The solution he advocates is that scientific witnesses should adopt some of the conventions of the Bar, by exchanging reports before the hearing, by consulting with each other, and having a duty to the Court to expose the reliability of their findings. Since I have spent some considerable part of this address urging precisely this last point, you will not expect me to disagree with his views. An Alternative Procedure I do think however that he is over-optimistic in his assumption that by these methods, conflicts between experts would be resolved. I n cases where this did not occur I believe that each expert should be required to present his views in court rather after the manner of a debate. Each would in turn make a statement and would later be able directly to question the other about points of disagreement. The experts would have an argument before the Court with the Judge as Chairman. No doubt this departure would not appeal to the legal pundits, but they should bear in mind that the ultimate purpose of court hearings is to assist the jury in determining guilt or innocence. Ordinary people, the jury, are very accustomed to hearing people argue, and to making up their minds on the basis of what they hear. I would go further and say that they are much more likely to get the truth of things as the result of this approach rather than by listening to conventional court proceedings which may well appear to them as some sort of tedious quiz-game, the rules of which are only plain to the initiated. There would be difficulties, but these could be overcome. An additional advantage would be that scientific experts, quite unusued to court proceedings (the expert on the effects of powerful magnetic fields on computer data stores, for example) would be able to present their evidence in a direct logical way and one to which they would be well accustomed. The fact that they would need to present it so as to be understood by non-scientists would rapidly expose the inadequacies of the kind of expert who conceals his alleged expertise behind a cloak of incomprehensible jargon. Such exposure would be to the general benefit of both Science and the Law. T o summarize then, I have attempted to show a number of important things that Science can do for the Law, provided the Law will let it. I t is for societies like ours to use its growing influence to make such things possible. References ORMROD, R., 1968, Criminal Law Review, 240. D., 1960, Science and the Courts, J. Forens. Sci. Soc., 1, 6. PATTERSON,
What can Science do for the Law? DAVID PATTERSON Department of Colour Chemistry, The University, Leeds, England
A Presidential Address delivered on the occasion of the Society's 15th Annual General Meeting in London on the evening of Friday, November 15, 1974. I n return for presiding in as impartial as possible a manner over the meetings of the Council of the Forensic Science Society, it was decided some three years ago that the President should be given the opportunity, in alternate years, of delivering to the Annual Meeting of the Society a Presidential Address. The first of these was duly given two years ago by my predecessor in this office, Dr. Julius Grant, and the subject he chose was Towards a New Profession? a title which he posed as a question. Now, one of the advantages of being an early speaker in such a series is that one is not restricted by the need to avoid topics that have been chosen by earlier Presidents. I have therefore selected the title also in the form of a question: What can Science do for the Law? This is indeed a very wide subject and I shall confine my remarks to a brief review of the period since the Society was formed in 1959, together with an attempt to look a little into the future. Both in my University employment, and as a magistrate, I am unused to consulting higher authority before expressing my opinions, since academic freedom and the independence of the judiciary are cornerstones of the pattern of British society. Neither can I claim to have consulted the Council of the Forensic Science Society as to what I should say, because I regard the independence of such scientific societies as ours, as of fundamental importance to the continuing health of Science and the development of our democracy, and this requires that there must always be on hand challenges to the existing orthodoxy in Science and in Government. For better or for worse then, what I am about to say is entirely a t my own responsibility. I n the opening address which I gave at the inaugural meeting of the Forensic Science Society a t the University of Nottingham in 1959 (Patterson, 1960), I attempted a definition of what constituted the main objects of forensic science, a t least as far as the criminal law is concerned. The essence of this was that what the Courts frequently wanted was a firm statement about the linkage between two objects. For example, did this fibre, paint chip, soil, wood, blood or whatever-something generally in small amount associated with a suspect, "the crime sample", come from a particular source known to be connected with a particular crime, "the control sample" ? Sometimes a definite answer can be given, but more often all that can be said is that the crime sample could have come from the control sample. I suggested that the number of examples where no clear answer could be given would be reduced by "refining methods so that smaller quantitative differences can be detected with certainty, and by the search for more subtle and unique links."
Sharpening the Tools Let us see what progress has been made since 1959 by a particular example. Suppose we are trying to see whether a bit of nylon filament found on a suspect's clothing came from a victim's garment. The first steps would be to establish that both were nylon of the same chemical structure (say Nylon 66 and not Nylon 6) ; that the denier and cross-sectional shape were the same (both circular). If the garment was dyed, then we would expect the crime filament to have the same colour under the microscope as control samples from the garment. This could all have been done in 1959, now we can go further.
I n the making of nylon itself a process called polymerization is used and to speed this up, substances called catalysts are added. These are metal salts of various kinds and their exact nature varies from manufacturer to manufacturer. Techniques are now available for identifying and measuring the amounts of these substances in single filaments. I n addition the transmission spectra of the single filaments can also be measured, removing an element of subjectivity from visual colour matching. Chromatography might also allow it to be said that the dyes used in garment and filament were identical, though here some partial interference with the crime sample would be necessary. The more properties that we can show are similar between crime and control samples, the greater the probability that the crime filament did come from the victim's garment. The process is similar to finding and increasing the number of points of similarity between crime and control fingerprints. I do not think that it will ever be possible to prove "beyond reasonable doubt" that a single filament came from a particular garment. But the more properties we can measure, the more we can eliminate other sources of the filament, pointing more and more definitely to the control source as being the true source or, on the other hand, of eliminating it, since as soon as any property is different, that source is eliminated. The value of the evidence of the identity of the two filaments is much higher if taken in conjunction with other non-scientific evidence. I t might be known for example that the shop had only sold six garments of the same type and colour in the town in question, and the other five could not possibly have been anywhere near the suspect. Such conjunction of scientific evidence and quite independently established facts can in my opinion build up a very strong case indeed against a suspect. I n practical terms, this means that the develoment of analytical methods for detecting increasingly specialized and increasingly minor constituents of fairly common materials, what I have termed "Sharpening the Tools" offers a powerful way in which Science can help the Law.
Some Difficulties Among the many new and powerful analytical tools introduced since the Forensic Science Society was founded, neutron activation analysis is one which perhaps best illustrates the difficulties which arise in the "sharpening the tools" approach. Many objects such as human hair contain minute quantities of metals which can be made radioactive by placing the object in an atomic pile. These tiny amounts can then be accurately measured. The presence of a number of these constituents in identical (though small) amounts seemed to be the ultimate in establishing the identity of origin of crime and control samples. But the method proved too sensitive. Variability of the analyses on samples along the length of a single hair and from place to place on an individual's head, still left difficulties in deciding that a single hair must have come from a particular head of hair. I n establishing the common source of specimens, then it is probably true that our tools are currently a little too sharp. Before we can exploit them, we need a much greater knowledge of the normal distribution of a large number of substances in our ordinary environment. Only then can we positively identify the abnormal as being outside this pattern. Fortunately, an increasing number of papers is appearing which provide this background information.
Scientific Offences I want to turn now to a second development in the field of forensic science which has occurred during the lifetime of the Society. It is the growth of the number of "scientific offences", by which I mean offences which are defined in terms of scientific measurements. Speeding in motor vehicles is the oldest and a new one is that of driving a motor vehicle with more than a prescribed amount of alcohol in the blood. Here there are fixed numerical thresholds for committing a n offence. I n built-up areas a speed of 29mph is unexceptionable, 3lmph means committing an offence. I n the blood, 79 milligrammes of alcohol per 100 millilitres of blood is blameless, 81mg alcoho1/100ml means loss of one's driving licence if one is caught. At least, so the law would have it, but everyone
knows in practice this is not so. Few prosecutions are brought for driving at speeds below 40mph or for blood alcohol contents below 95mg/100ml. Many years ago a colleague of mine sent a sample to a senior and respected analyst in a large chemical company. When he went to get the result he enquired what the error in the measurement was. The analyst was a Yorkshireman, he stuck his thumbs through his braces and with his feet on his desk retorted, "errors lad, we don't have errors, when ah gives tha a number that's it !" This is rubbish, of course, despite his eminence. There are well-known statistical laws governing the errors in repeat measurements of any quantity. The spread of values can be found by experiment, and the spread is characterized by the standard deviation. 95% of all measurements fall in a range of plus or minus twice the standard deviation. Thus if the true value were 8,O units and the standard deviation were 2 units, by this analytical method 95% of measurements would lie in the range 76-84 units; 99% lie in the range 74-86 units. What I have said applies to the errors in the actual analysis and there will be others which we will ignore for the moment. We are clearly not going to convict those who get an analytical answer below the legal limit, that is, those who whilst actually having 81 units, get results below this. What of those with a n actual amount of 80 units who get above 80? Justice clearly demands that no one should be convicted because of analytical errors. It has become customary for results to be reported as "not less than xmg alcoho1/100ml of blood", and as I said earlier 95mg seems to be the accepted level for prosecutions to be brought in courts where I sit. This allows such a margin for error that no one who is innocent should be convicted. We can expect the number and variety of scientific offences to increase. For one thing, such cases are very easy to decide; even the least numerate will not often be in error about deciding whether one figure is greater than another. I t is child's play compared with deciding whether a driver has exercised "due care and attention" when associated with a road accident. But there are more cogent reasons than this for expecting the number of scientific threshold offences to rise. I n an increasingly technological society we may expect many more regulations and laws concerning the permissible limits of chemicals in our environment-for example the quantities of colourants and additives in food, the amounts of sulphur dioxide in the air and the amounts of lead and carbon monoxide from vehicle exhausts. Then there is the futuristic offence of "Wilfully exposing the magnetic store of a computer to a field of x thousand gauss to the peril of the national records . . .". The proof of guilt in other offences may depend on the detection of small amounts of drugs and explosives. I n these instances we want to know the limits of detection of the materials in question by the analytical methods used, as opposed to the confidence limits on numerical results, since we can't go along with the eminent Yorkshire analyst and his touching but incorrect belief in accuracy. The second point I want to make, therefore, is that while Science can aid the law by defining offences in objective numerical terms, there should always be freely admitted and disclosed figures on the accuracy of the measurements involved in the securing of convictions for those offences.
No M o r e Cross-Examination Finally, I want to suggest something that the Law could do so that it may benefit fully from the assistance Science can givc it. I t concerns the treatment of scientific evidence in Courts. I am sure that what I have to suggest will have little immediate support from the legal profession. I n an accusatorial system of trial, cross-examination of witnesses is an essential part. Skill in it brings the highest reputations and rewards in the profession of the advocate. I t may well be the best method of wringing the truth from lying villains; I think it probably is, but I also think that the methods of cross-examination are quite inappropriate to the assessment of scientific evidence.
There will seldom be disputes between scientific experts on the results of scientific tests, not if the methods are exposed to the scrutiny of the widest scientific circles, as they should be. Even if there is, I still do not consider that cross-examination is appropriate. The most likely cause of dispute is the inference to be drawn from the results. I am not alone in my opinion that crossexamination is inappropriate in testing scientific evidence. Sir Roger Ormrod in a very perceptive article (Ormrod, 1968) said of cross-examination: "The questioner is dominant. The form of his questions conditions the form and often the content of the answers;" and later "Questions which contain hidden assumptions sometimes yield answers which almost contradict the witness's real meaning unless he is quick enough to detect and expose the assumption." There is obviously something seriously wrong when such a situation can occur. I n the same article, some possible solutions were propounded. One is the appointment of Court experts, possibly from an approved panel, to assist the Courts. Such a system appears to apply in California, since one of the stated aims of our sister society the California Association of Criminalists is to "Provide a board of review in cases involving differences of professional opinion when requested." Sir Roger's opinion is that such a system is unlikely to be acceptable in criminal cases in this country. The solution he advocates is that scientific witnesses should adopt some of the conventions of the Bar, by exchanging reports before the hearing, by consulting with each other, and having a duty to the Court to expose the reliability of their findings. Since I have spent some considerable part of this address urging precisely this last point, you will not expect me to disagree with his views. An Alternative Procedure I do think however that he is over-optimistic in his assumption that by these methods, conflicts between experts would be resolved. I n cases where this did not occur I believe that each expert should be required to present his views in court rather after the manner of a debate. Each would in turn make a statement and would later be able directly to question the other about points of disagreement. The experts would have an argument before the Court with the Judge as Chairman. No doubt this departure would not appeal to the legal pundits, but they should bear in mind that the ultimate purpose of court hearings is to assist the jury in determining guilt or innocence. Ordinary people, the jury, are very accustomed to hearing people argue, and to making up their minds on the basis of what they hear. I would go further and say that they are much more likely to get the truth of things as the result of this approach rather than by listening to conventional court proceedings which may well appear to them as some sort of tedious quiz-game, the rules of which are only plain to the initiated. There would be difficulties, but these could be overcome. An additional advantage would be that scientific experts, quite unusued to court proceedings (the expert on the effects of powerful magnetic fields on computer data stores, for example) would be able to present their evidence in a direct logical way and one to which they would be well accustomed. The fact that they would need to present it so as to be understood by non-scientists would rapidly expose the inadequacies of the kind of expert who conceals his alleged expertise behind a cloak of incomprehensible jargon. Such exposure would be to the general benefit of both Science and the Law. T o summarize then, I have attempted to show a number of important things that Science can do for the Law, provided the Law will let it. I t is for societies like ours to use its growing influence to make such things possible. References ORMROD, R., 1968, Criminal Law Review, 240. D., 1960, Science and the Courts, J. Forens. Sci. Soc., 1, 6. PATTERSON,
