Forensic Science and the Law

Although the definition of forensic science may be debated, the relationship of forensic science to the law is clear. Without the judicial system, the crim- inalist has no function. The job of the analyst is to provide scientific infor- mation to the legal community and, in doing so, to translate the story the evidence has to tell. The scientific analysis is only performed at the behest of someone seeking to introduce the evidence into a court of law. This could be an investigator or the prosecuting attorney. It could also be the defendant through a defense attorney. The evidence comes to the forensic analyst because someone has deemed it relevant to the reconstruction of an event in time, an event that is associated with a suspected crime.

The frequently opposing aims of science and law must be acknowledged before they can be surmounted. While the scientist is trained to be objective to the point of skepticism, and to present alternative explanations equally, the U.S. legal system is constructed around a system of advocacy. The pros- ecution is expected to strongly argue the case that she at least believes to be the truth, and the defense attorney is required to strongly advocate for his client and may elect to emphasize the interpretation that best supports his position. These contradictory goals frequently make for an uneasy alliance between science and law, with both representatives battling to maintain their own professional ethics. Each case presents these challenges anew.

1. What Is the Question?

If you don’t ask the right question, you won’t get the right answer, no matter how brilliant your analysis. Although that aphorism could describe most situations in life, its consequence becomes excruciatingly clear when applied to a case investigation. Asking the right question will be a continuing theme throughout this book.

a. Translating the Legal Question into the Scientific Question

Before the criminalist ever picks up a magnifying glass, pipette, or chemical reagent, he must have an idea of where he is headed; he must define a question that science can answer. That question is determined by the circumstances of each individual case and calls into play the experience, education, and knowledge of the analyst. It is critical to understand that this question depends directly on the legal question framed by the investigator or attorney. In a criminal action, these all derive from the legal definition of the crime itself and in some cases from the circumstances surrounding the crime. For the legal action to proceed, the law must establish that a crime has, in fact, been committed by defining the corpus delecti (literally, “body of the crime”). All of the elements that legally define any particular crime must be present

16 Principles and Practice of Criminalistics

to proceed. In this setting, the only germane questions are the legal questions. The role of the forensic scientist is to translate the relevant legal question into a scientific question. If this cannot be done, then forensic science has no role to play.

One way the criminalist can assist law enforcement and legal profession- als is by helping them to translate a legal question correctly (Did O. J. Simpson kill Ron Goldman and Nicole Brown Simpson?) into a question that science can answer (What genetic types are found in the bloodstains from the scene?). The answer to the scientific question will then assist in answering the legal question. Conversely, one of the most effective counters to the presentation of physical evidence is to show that the wrong question was asked. For instance, finding the suspect’s blood on the suspect’s shoes is irrelevant to whether he attacked the victim. Similarly, the finding of an unusual collection of fibers on the murder weapon becomes meaningless if both the suspect and the victim were wearing uniforms composed of the rare fiber set. Analysis of physical evidence in a crime laboratory is best suited to answering who, what, where, and how; it is less adept at answering

when and can almost never answer why. Because the design or selection of appropriate tests depends completely on the initial hypothesis, it must be carefully framed at the beginning of the investigation rather than on the witness stand.

It is crucial to note that the moment the question is translated into science, the component of guilt or innocence is lost. Forensic science seeks to establish connections (or lack thereof) between evidence and its source, and secondarily, between items that may be associated by the evidence. Said in another way, we consider the probability of the evidence in light of com- peting hypotheses, often the prosecution’s allegation and the defense prop- osition. Guilt or innocence may only be considered by the legal system and decided by a judge or jury.

The focus of an analysis and its interpretation are dictated by the cir- cumstances of the case and the question(s) facing the criminal justice system. This is the reason the most common and useful answer to any general crim- inalistics question is, “it depends.” The analysis of a sexual assault case serves as a good example of this point. Sexual assault, and rape in particular, is distinguished from other crimes in that it is not necessarily evident by mere observation that a crime has occurred. We know that if we come home, the window has been forced open, and our stereo is missing, that a burglary has taken place. This is generally obvious to any other observer as well. It is rarely possible to look at a woman or man and determine that she or he has been raped. The crime of rape can be summarized as the act of sexual intercourse accomplished through fear or force. Science can assist in substantiating one of the elements (that of sexual intercourse) by determining that sperm are 8127/frame/ch01 Page 16 Friday, July 21, 2000 11:32 AM

present. This, of course, says nothing about the fear or force part. The mean- ing of the scientific finding may change dramatically depending on the cir- cumstances of the case.

The use of science in the arena of civil law has grown as pioneering and developing societies have achieved the economic stability necessary to sup- port elective activities. Civil litigation almost always concerns money; to argue about it, one must have both the time and means to do so. Many of the common areas of civil litigation, such as medical malpractice, money fraud, and engineering, are outside the scope of this volume. Of the areas of inquiry shared by criminal and civil investigations, the legal standards obvi- ously differ, leading to, among other things, different questions, but the scientific analyses remain the same.

b. Physical Evidence and Circumstantial Evidence

Before we proceed further, it is worth reviewing the concepts of circumstan- tial evidence and physical evidence. Most physical evidence is circumstantial evidence — that is, its involvement in the scenario requires some further inference or assumption. Exceptions to this generality include substances that by their very presence are illegal, such as illicit drugs. Circumstantial evidence need not be physical, although most of it is. The term circumstantial evidence carries with it the connotation of untrustworthiness, while eyewitness evi- dence tends to be considered conclusive. Nothing could be farther from the truth. In fact, numerous studies have shown eyewitness evidence to be remarkably unreliable (Loftus, 1996).

Consider the following scenario. You are camping in a cabin deep in the woods in Alaska. It is the depth of winter and the snow pack is many feet. You hear a sound in the middle of the night and go to the window to see what it is. The moon is new, and it is practically pitch dark. You see a quickly moving shadow that seems to blend in with the snow. Is it a polar bear? Is it a potential burglar dressed in white? You really can’t be sure. In the morning you venture outside to behold — very clear snowshoe tracks. There is no question in your mind that the previous night’s visitor was a human, not a bear. You then also notice that the lock to your toolshed is hanging open, and a reconnaissance of the interior reveals that some of your tools are missing. Which evidence was more convincing — your midnight glimpse (eyewitness evidence) or the prints in the snow (circumstantial evidence) combined with the burglary? More important, which evidence will be more convincing to the local police — your description of a dark blur or casts of the tracks in the snow. Even if you had had a really good look at the burglar, it’s still your word against his; the physical evidence of the tracks is inarguable. (The issue of the significance of a match to the suspect’s snowshoes is another issue). So much for the assertion that “the evidence is only circumstantial.”

18 Principles and Practice of Criminalistics

C.

Summary

In writing this book, we found that our subject area logically divided itself into three sections. In Section 1, Background and History of Forensic Science, we introduce you to definitions and concepts to that we will refer throughout the book. We also spend some time looking backward to see how the evolu- tion of forensic science can help us understand the issues we face today. In Section 2, The Principles of Forensic Science, we introduce you to a unifying paradigm for thinking about forensic science. Included in this paradigm is a new principle, divisible matter, that we propose is necessary to invoke the well-known principle of transfer, attributed to the great forensic scientist Edmund Locard (Locard, 1920). We also discuss at length the forensic prin- ciples of identification, classification, individualization, association, and recon- struction. In Section 3, The Practice of Forensic Science, we address some of the pragmatic issues facing the criminalist today. We start with recognizing an item as evidence, progress through analysis and interpretation guidelines, and finish with a discussion of ethics and accountability. We hope we have at least intrigued you to read further.

References

Ashbaugh, D. R., Quantitative–Qualitative Friction Ridge Analysis: An Introduction to

Basic and Advanced Ridgeology, CRC Press, Boca Raton, FL, 2000.

Bacon, F., The Great Instauration. Originally published 1620, The Great Instauration and the New Atlantis, Weinberger, J., Ed. AMH Publishing Co., Arlington Heights, IL, 1980.

Ceccaldi, P. F., From crime to evidence, Int. Police J., 1974.

Cole, S., Witnessing identification: latent fingerprinting evidence and expert knowl- edge, Soc. Stud. Sci., 28(5–6), 687, 1998.

Cole, S., What counts for identity? The historical origins of the methodology of latent fingerprint identification, Sci. Context, 12(1), 139, 1999.

Daubert v. Merrill Dow Pharmaceuticals, 509 U. S., 1993.

Decartes, R. Discourse on Method, 1637.

Doyle, A. C., The Adventures of Sherlock Holmes: A Scandal in Bohemia, The Strand

Magazine, 1891.

Evett, I., What is the probability that this blood came from that person? A meaningful question? J. Forensic. Sci. Soc., 23, 35, 1983.

Fisher, R. A., The Design of Experiments, Oliver and Boyd, London, 1949.

Hofstadter, D. R., Gödel, Escher, Bach: An Eternal Golden Braid, Basic Books, New York, 1979.

Horgan, J., The End of Science, Addison-Wesley, New York, 1996.

Jones, L. V. and Gabard, C., Scientific Investigation and Physical Evidence; Handbook

for Investigators, Charles C Thomas, Springfield, MA, 1959. Kumho Tire Co., Ltd., et al. v. Carmichael. 97-1709 U.S., 1999.

Locard, E., L’enquete Criminelle et Les Methodes Scientifique, Ernest Flammarion, Paris, 1920.

Loftus, E. F., Eyewitness Testimony, Harvard University Press, Cambridge, MA, 1996. Maddock, J., No evidence for cold fusion neutrons, Nature, 340, 1989.

Murdock, J. E. and Biasotti, A. A., The scientific basis of firearms and toolmark identification, in Firearms and Toolmark Identification, in Modern Scientific

Evidence, Faigman, D. L., et al., Eds., West Law, San Francisco, 1997.

Naess, A., Book review, New Scientist, August, 1998.

Neyman, J. and Pearson, E. S. On the use and interpretation of certain test criteria for purposes of statistical inference, Part I and II, Biometrika, 20, 174–240, 263–294, 1928.

Popper, K. R., Conjectures and Refutations: The Growth of Scientific Knowledge, Basic Books, New York, 1962.

Stark, P. B., SticiGui© Glossary of Statistical Terms, 2000, available at

http://www.stat.berkeley.edu/~stark/SticiGui/Text/gloss.htm#n.

Taroni, F., Champod, C., and Margot, P., Forerunners of Bayesianism in early forensic science, Jurimetrics J., 38, 183–200, 1998.

Thornton, J., The DNA statistical paradigm vs. everything else, correspondence,

J. Forensic Sci., 42(4), 758, 1997.

Van Heerden, T. J., Criminalistics, University of South Africa, Muakleneuk, Pretoria, 1982.

Webster’s Encyclopedic Unabridged Dictionary of the English Language, Gramercy

Books, New York, 1996.

Williams, E. W., Modern Law Enforcement and Police Science. Charles C. Thomas, Springfield, MA, 1967.

21

The Evolution of