Failed Evidence: Why Law Enforcement Resists Science

2. Science and Traditional Police Investigative Methods: A Lot We Thought We Knew Was Wrong

18 > 19 imaging to gain intelligence or find the defendant. But interrogations of suspects, identification by eyewitnesses, and forensic testing make up the most common aspects of evidence gathering. The science of the past several decades has taught us that much of the common wisdom concerning these types of evidence turns out to be wrong. What’s more, misconceptions about these methods have caused miscarriages of justice—cases in which juries have convicted innocent people. Forensic Science: Is It Really Science, or Something Less? For years, forensic scientists have used science and the tools of the laboratory to help police officers and prosecutors find evidence that could help build the case against an accused. The identification of materials, such as suspected contraband substances or trace evidence like gunpowder residue, makes use of classic techniques of chemical analysis. The matching of bullets to particular guns utilizes microscopic examination; so does the forensic comparison of hairs and fibers. Arson investigators apply knowledge of the way fire starts and burns, and the way various substances can serve as fuel or accelerants. Serologists give us information that allows us to know whether the blood found at the scene might have belonged to the suspect under scrutiny. Other specialists use their expertise to match shoeprints to particular shoes, tire tracks to particular tires, and bite marks to the teeth of specific individuals. Fingerprint analysis tells us that the impressions of the unique ridge patterns that make up each person’s fingerprint may be “matched” for identification purposes. This has long represented the gold standard in forensic science: fingerprint analysts with sufficient training, knowledge, and expertise could match a print left by an unknown person at a crime scene to a known sample. Perhaps only the perpetrator and the victim of the crime had been present when the crime occurred, but with fingerprint analysis—and other forensic disciplines—the forensic scientist would know who did the crime. But DNA testing changed almost all of this: it upended the certainty and the safe assumptions that forensic science had rested on for almost a century. Most of forensic science had not, actually, come from true scientific work or the experimental laboratory. Rather, the forensic disciplines other than DNA and chemical analysis originated with criminal investigation, not the scientific method. Many of the common forensic science disciplines “have never been exposed to stringent scientific inquiry” to gauge their accuracy, limitations, and foundations.1 This means that these methods do not really qualify as science, and thus do not deserve the kind of respect that the law 20 > 21 Andrew Taslitz, a law professor at American University and an expert in the law of evidence and criminal procedure, recalls that he once presented the latest social science findings on eyewitness identification at a state’s annual seminar for all of its judges.3 Taslitz presented the judges with all of the most important scientific work on eyewitnesses from leaders in the field, and discussed new procedures that the research suggested would make for more accurate identifications. During the question and answer period, one judge in the audience raised his hand. “All of this, everything you’ve said, that’s just social science, isn’t it?” The judge continued, “You can make social science say anything you want. I’m not going to give any credence to that.” Taslitz remembers that not all the judges agreed with the man, but “there were a significant number of judges who were totally with this guy.” Taslitz argued with the judges, explaining what makes good science and how such work is done, but he encountered “real skepticism.” Experiments in the social sciences, dismissed by these judges as soft or not real science, can be just as rigorous, as reliable, and as important as any experiment done with a flask full of chemicals. When performed according to the principles and procedures of the scientific method, social science is unambiguously real science. This becomes critically important because much of what science can tell us about how basic aspects of police investigation actually work—for example, how utilizing eyewitnesses in certain ways raises the risk of false identifications—comes from social science, particularly cognitive and behavioral psychology. Though the judges described in Professor Taslitz’s story might consider this work soft and unworthy of acceptance, it exhibits all of the principles of scientific investigation described here: reliance on data, not intuition; the development and testing...