Barry A.J. Fisher in 1980. In a new article in the journal Forensic Sciences Research, Fisher argues the importance of subjective witness expertise, and that not all evidence can be quantified. (Photo: Courtesy of Barry A.J. Fisher)

A trend in forensic science is to quantify as much evidence as possible, from the DNA population statistics to the margin of error on fingerprint matching and toolmark comparisons.

But an expert witness, who spends their entire career analyzing trace evidence, also has a role in the courtroom, argues a former crime lab director in the journal Forensic Sciences Research.

A reminder now is crucial at this moment of debate over the “forensic overhaul,” argues Barry A.J. Fisher, the former director of the Los Angeles County Sheriff’s Department Crime Laboratory. As the scientific foundations for some forensic disciplines have been questioned, the arguments should still focus on whether expert testimony bears the weight of experience and accuracy, writes Fisher.

“The reader might well think that the information in this commentary does not really cover much new ground,” Fisher writes. “However, this writer suspects that new forensic examiners as well as new prosecutors may not have considered this issue, and may get caught up in an evidentiary hearing with the goal of excluding certain physical evidence.”

The “Daubert” standard of having judges be the “gatekeepers” to expert witnesses (established in a 1993 U.S. Supreme Court case) applies to non-quantitative measures, Fisher writes.

Pattern evidence such as fingerprints, firearms, toolmarks, footwear, tire impressions, handwriting, bitemarks and other analysis should not be immediately relegated to “junk science,” the retired crime lab director argues.

Fisher is the author of Techniques of Crime Scene Investigation, a criminalistics textbook published by CRC Press. He has written for, and been interviewed by, Forensic Magazine multiple times.

“Not everything can be quantified,” Fisher said, according to a feature last year.

In his latest piece, Fisher summarizes some of the criticisms which have led to the “forensic overhaul” in recent years. First, the 2009 National Academy of Sciences report “Strengthening Forensic Science in the United States: A Path Forward” established where certain areas needed further scrutiny. The report resulted in the creation of the National Commission on Forensic Science and the Organization of Science Area Committees for Forensic Science, known as OSAC. The former was disbanded by the Trump administration in April, but the latter continues to propose and codify new standards in American laboratories and courtrooms. Another milestone was the additional report by the President’s Council of Advisors on Science and Technology (PCAST), which reiterated some of the same grievances last fall.

But Fisher cites one of the foremost applications of Daubert in case law: the 1999 decision Kumho Tire Co. v. Carmichael. Objective data could only help expert testimony—but lacking it doesn’t necessarily exclude the value of the expert’s insight, Fisher explains.

“Many experts offer their conclusions in legal matters based on their professional training, knowledge, skills and experience. Often that knowledge is based on empirical data,” writes Fisher. “Consider, psychologists who offer opinions about syndrome evidence, or forensic pathologists who offer opinions on the manner and means of death. Medical practical practitioners base diagnoses on practical experience, which may not have much statistical data to support conclusions.

“Practitioners would call that professional expertise,” he adds.

The nation’s top law enforcement agency has been appropriately handing chemical and trace evidence to meet accreditation and scientific standards at the FBI Laboratory, the U.S. Government Accountability Office revealed in an audit and report of the Bureau released Wednesday. The one recommendation: the agency could review more of its examiners’ testimonies to continually monitor the end product in court, the GAO concludes.