There is no “individualization,” but there is “identification”—albeit with limits. And while an ink fingerprint on a check being cashed at an FDIC-insured bank is a relatively simple comparison, a bloody palmprint on concrete poses many more complex challenges to expert forensic examiners.

The Department of Justice rolled out “uniform language” last week in how federal fingerprints experts should tell juries about what they found in the minutest details of ridge patterns, whorls, scars and even pores. The experts should explain their work, without expressing “scientific certainty” or trying to calculate the incalculable—and that includes avoiding “individualization.”

Such rules have gradually been implemented anyway, according to the International Association for Identification, the largest group representing fingerprint experts.

“There’s nothing earth-shaking in here—it’s something we’ve been doing,” said Bill Schade, biometrics records manager at the Pinellas Sheriff’s Office in Florida, and IAI spokesman, in an interview with Forensic Magazine. “That’s what this is all about: not using ‘trigger words,’ not misleading the jury because they hear the ‘magic word.’ We support that, of course.”

The new rules indicate that examiners can make three conclusions: source identification, inconclusive and source exclusion.

Source identification is an inductive inference, but reaches the probability that two impressions were made by different sources is “negligible.”

An examiner may “not assert a 100 percent level of certainty,” or make any other numerical assertions. That includes avoiding making claims of infallibility, or a “zero-percent error rate.” The quantitative representations to avoid would also include citing the number of comparisons and cases the expert has performed over the course of a career.

As with other recent guidelines in the forensic sciences, the terms “reasonable degree of scientific certainty,” “reasonable scientific certainty” and related paradoxical terminology must be avoided, according to the uniform language.

Schade, a well-known veteran of 46 years in the fingerprint discipline, spoke separate from the IAI statement about his personal take on what he called the “constant evolution” in the discipline. Schade said training was different in the 1970s and 1980s when he was just beginning. The adversarial system meant that experts would put their best prints forward—they would tell juries about the strengths of their comparisons, he added.

Now the importance is of explaining methodology—even if that means explaining to lay persons both the characteristics of Level 2 comparisons like ridge endings and bifurcations, as well as Level 3 features like pores, ridge deviations, breaks and creases.

“Let’s let the jury, and the defense know,” said Schade. “I’m not sure it’s the words—I think you need to explain to the jurors the risky calls, and the confident calls.”

Indeed, latent fingerprint identification was one of the disciplines criticized in a pair of documents that bookended the two terms of the Obama Administration: the 2009 report by the National Academies of Science entitled “Strengthening Forensic Science in the United States: A Path Forward,” as well as the 2016 document issued by the President’s Council of Advisors on Science and Technology, or PCAST. Both reports contended that fingerprints are not sufficiently quantitative in many cases.

However, latent fingerprint identification is one of the disciplines that has proven to be consistently accurate. A critical paper published in 2005 identified 22 fingerprint misattributions internationally over the first century of the use of forensic fingerprint comparisons. Ten of those resulted in convictions that were later overturned. None of those convictions were reached after 2000.

Schade said latent fingerprints have been improving methods, alongside the better tools like imaging and algorithms.

“It’s a constant evolution. It’s getting better—and it’s getting more fair,” Schade added.