U.S. Deputy Attorney General Rod Rosenstein defended several questionable forms of forensic evidence Tuesday. "Most of you work on the front lines of the criminal justice system, where forensic science has been under attack in recent years," Rosenstein said in a speech at the National Symposium on Forensic Science. "Some critics would like to see forensic evidence excluded from state and federal courtrooms"

Over the past two decades, DNA testing has revealed hundreds of wrongful convictions, many of them stemming from "pattern" evidence such as bite marks, shoe prints, and microscopic hair comparison.

The Justice Department has been under pressure to improve forensic standards since it and FBI admitted in 2015 that two dozen examiners in one of its hair analysis labs had given flawed testimony in hundreds of cases. In those cases, 32 defendants were sentenced to death; 14 were eventually executed or died in prison.

In 2016, the President's Council of Advisors on Science and Technology (PCAST) released a report finding "a dismaying frequency of instances of use of forensic evidence"—such as analyses of hair, bite marks, and shoe prints—"that does not pass an objective test of scientific validity."

But the Justice Department, under both Barack Obama and Donald Trump, has rejected calls to stop relying on such evidence. In his speech Tuesday, Rosenstein continued to defend them:

Many of the challenged methods involve the comparison of evidence patterns like fingerprints, shell casings, and shoe marks to known sources. Critics argue that the methods have not undergone the right type or amount of validation, or that they involve too much human interpretation and judgment to be accepted as "scientific" methods.

Those arguments are based on the false premise that a scientific method must be instrument-based, automated, and quantitative, excluding human interpretation and judgment. Such critiques contributed to a recent proposal to amend Federal Rule of Evidence 702 for cases involving forensic evidence. The effort stems from an erroneously narrow view of the nature of science and its application to forensic evidence.

Forensic science

Forensic science is not only quantitative or automated. It need not be entirely free from human assumptions, choices, and judgments. That is not just true of forensic science. It is also the case in other applied expert fields like medicine, computer science, and engineering.

Betty Layne DesPortes, a Virginia criminal defense attorney and past president of the American Academy of Forensic Sciences, is troubled by Rosenstein's comments on court challenges to evidence. 

Drew Findling, president of the National Association of Criminal Defense Lawyers (NACDL), points out that his organization has worked for several years with the Justice Department, the FBI, and the Innocence Project to review flawed microscopic hair comparison analysis and notify defendants who this evidence was used against.

"Given this context, we are concerned about [Rosenstein's] comments that pattern evidence that does not have sufficient foundational validity may be offered solely based upon 'human assumptions, choices and judgments' instead of science," Findling says. "NACDL is concerned that the remarks could lead to a policy that will leave the door open to unreliable forensic evidence."

The National Commission on Forensic Science (NCFS), an independent review group formed by the Obama administration, released a draft code of ethics for forensic science providers.

The draft code included a mandate to inform all parties, including defendants and victims, when misconduct or a lack of professional standards adversely affected a case.

But when Lynch adopted the new code of ethics in a 2016 memo, it only required forensic providers to "inform the prosecutors involved of material nonconformities or breaches of law or professional standards that adversely affect a previously issued report or testimony."

Last April, the Justice Department, now under Attorney General Jeff Sessions, chose not to renew the NCFS's charter, effectively shuttering the group. At the commission's final public hearing, Keith Allen Harward, who spent 33 years in Virginia state prison for rape and murder before being exonerated by DNA evidence, testified.

The Justice Department replaced the commission with new working groups, but former members of the NCFS and others in the field worry that these are essentially in-house and will lack the NCFS's independence.

Rosenstein's comments are a shame, DesPortes says because almost everyone welcomes many of the improvements he announced, such as introducing rules about what language forensic experts can use while testifying.

"The ironic thing is, I think both sides agree that the steps being taken are good steps," DesPortes says. "We all agree on what to do, it's just we don't agree on how each side is characterizing the battle. When both sides do that, walls go up and things become more difficult."