HF: People tend to think of police forensics as highly scientific and of confessions and eyewitness testimony as highly reliable. Your book, however argues that the “bottom line” is that “most of forensic science lacks a basis in science,” a finding that has a National Academy of Sciences report to back it up. You also point out problems with eyewitness identification and confessions to police. What has gone wrong with the use of evidence in the criminal justice system?

DAH: Most of what we call forensic science did not begin in any kind of traditional scientific setting, using the scientific method; these forensic procedures came from police investigation efforts, refined in police laboratories. Therefore, most of them bore none of the safeguards and guarantees of traditional science, and did not function that way. They were based on human experience and judgment, not data-grounded work; they were intuitive, rather than experimentally based. The conclusions of the National Academy’s 2009 report were only surprising for people outside the scientific community: With the exception of DNA-based identification, procedures that had always been called forensic science were not science at all, in any real sense. The emperor had no clothes.

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Because there was no scientific basis for most of these procedures, forensic testing was not anything like as reliable as most people had thought; errors were made and not caught; new (and ultimately completely unreliable) forensic methods, such as bite mark analysis and hair analysis, were introduced and used, without any kind of validation, with disastrous results. In addition, we have learned much about the errors unintentionally introduced by traditional law enforcement procedures using traditional methods of eyewitness identification and suspect interrogation.

Contemporary social science has taught us how to do a much more accurate and defensible job in both of these core law enforcement areas, with adjustments such as sequential blind lineups and the PEACE method of interrogation. It is the failure to follow these new, better methods, and to accept questions raised about forensics, that leave law enforcement and prosecutors vulnerable to unintentionally creating more wrongful convictions as we go forward, instead of fewer.

HF: Your book points out the various cognitive biases that can lead police and prosecutors to make mistakes. It also argues that cognitive biases, fears about changing the balance in the criminal justice system, and professional identity formation have led police and prosecutors to oppose science-based reform? What are these beliefs and biases and how do they work?

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DAH: Cognitive biases keep us trapped in faulty thinking by blinding us to certain realities or facts, and predisposing us to accepting others that may not be valid. Fears about shifting the balance in the way that the system works is common to many professions and pursuits; most of us have figured out how to cope within the professional and social worlds in which we work, and we fear that change in them will undermine our ability to keep doing what we do or may undermine our status or expertise.

Police and prosecutors are no different than people in other professions in this regard; change can be disorienting and even frightening. Some of them clearly see how important it is for better science and procedures to guide what they do, and are willing to make changes based on what we know now, instead of clinging to what we’ve always done. For example on the subject of recording suspect interrogations, even the FBI, which resisted this important and necessary best practice, has moved to recording interrogations. But a considerable share of the law enforcement community still resists change.

The problem is that resistance to change in enforcing the law and seeking justice in courts is not like resisting change in other pursuits. Not getting things right — not necessarily getting things perfect (no one expects that) but as right as a human system can, given the best knowledge we have — can have grave consequences for individual suspects and defendants (who can lose their freedom), can deprive victims of real justice, and can leave actual perpetrators on the street to victimize others when the wrong people go to jail, because of flawed procedures.

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HF: Your book was published before the establishment of the National Commission on Forensic Science, which is now being abolished by Attorney General Jeff Sessions. How has this commission responded to the challenges that you and others, including the National Academy, have pointed to?

DAH: The commission and its various actions and initiatives represented a real opportunity to confront some of the problems pointed out by the NAS report, and it was a chance for real progress — perhaps not as much as some would have liked, but forward movement nonetheless, in an absolutely crucial set of issues of criminal justice policy. The commission had taken on many of the challenges pointed out by the NAS report, and was moving toward crucial recommendations.

Abolishing it will only set back efforts to move law enforcement and prosecution closer to what science knows. That gap, between what we know and what our institutions do, may now grow instead of shrink, and inevitably, a price will be paid in the form of inaccurate verdicts, wrongful imprisonments, and a further deterioration in the credibility and integrity of the system.

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HF: Some of the commission’s work involved consideration of common standards for forensic evidence. What role do standards play, and how does the United States differ from other countries in its approach to standards?

DAH: Other countries have standards that apply to their law enforcement and prosecution agencies that we do not. For example, for years the United States had no standards concerning the proper number of points of similarity between two fingerprints in order for an expert to declare that they were from the same source. Other countries had a particular number that was required. In part, this was because of the massively decentralized law enforcement system of the United States, which is the opposite of most countries; the U.S. Department of Justice, for example, can only set standards for federal law enforcement, and state and local agencies are free to ignore them and set their own.

HF: To what extent, given publicly available evidence, is the disestablishment of the commission and other review procedures motivated by the skepticism of law enforcement and prosecutors that your book identifies?

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DAH: I believe that the abolishing of all of these efforts to create improvement in forensic procedures has a strong basis in the skepticism of a core of police and prosecutorial leadership in this country. Simply abolishing these efforts will not, of course, change the direction or results of current or future scientific inquiry into whether traditional approaches do or do not work well. The knowledge about problems and issues that have arisen with them, and the skepticism of courts for the more traditional methods, is now strongly rooted and growing.

These moves by the attorney general may slow progress toward what we know or will learn about the best ways to investigate, whether using forensic practices or police practices like suspect interviews, may be slowed, but that progress cannot be stopped. The era in which judges, juries, defense lawyers, the public and the media simply accepted these methods without question has now passed. Those who wish to derail change win a short-term victory through the attorney general’s unfortunate decisions here, but in the long run, it is no victory for them, for crime victims, for defendants or for the integrity of the criminal justice system.