Is Fingerprint Evidence Sound Science?

We carry around unique maps of swirls and ridges on our fingertips, and judges and juries have been using them for almost a century to decide innocence and guilt. Because no two people have the same patterns, fingerprint evidence has been nearly irrefutable in courtrooms for decades — until now.

A federal judge in Philadelphia has become the first to question the scientific soundness of fingerprint evidence.

U.S. District Court Judge Louis H. Pollak last week ruled that such evidence does not meet standards of scientific scrutiny established by the U.S. Supreme Court, and said fingerprint examiners cannot testify at trial that a suspect's fingerprints "match" those found at a crime scene.

The interpretation of fingerprint evidence has already been the source of heated debate in the forensic community, and Pollak's decision, coming after two years of legal challenges around the country, is likely to stoke the controversy. At issue is not whether a fingerprint is a unique identity marker, but whether fingerprint experts have scientifically sound techniques in determining identity from even a partial smudge of a fingerprint found at a crime scene.

Ruling Could Spawn Similar Cases, Decisions

Pollak's decision only applies to a murder trial scheduled to start later this month in Philadelphia — and shouldn't affect past convictions based on fingerprint evidence — but experts say it likely will have broad resonance. The ruling could serve as a basis for similar decisions in other courts and prompt further legal challenges based on its reasoning.

In the Philadelphia case, lawyers for three men accused of running a drug ring associated with four murders sought to bar fingerprint evidence from their upcoming trial. Pollak allowed fingerprint evidence to be presented to the jury but will not permit experts to testify that the crime scene prints "match" those of the defendants.

There is no "scientific testing that tended to establish the reliability of fingerprint identifications," Pollak ruled. However, Pollak did not reject the overall use of fingerprint evidence, saying witnesses could discuss similarities and differences between fingerprints and that the imprints are "permanent" and "unique."

In his ruling, Pollak relied on a 1993 U.S. Supreme Court decision that required judges to take a more direct role in deciding what scientific evidence could be permitted at trial. The court established the "Daubert" guidelines, which are designed to prompt questions about the scientific sturdiness of certain types of evidence, such as whether it has been adequately tested, what its error rate is, and, in the case of fingerprinting, whether there are standards for what constitutes a "match."

Handwriting, Hair Evidence Also Questioned

Fingerprints have been used in courtrooms since the early 20th century, and judges have generally regarded them as scientifically sound. In reality, says evidence expert Jennifer Mnookin, the use of fingerprinting has never withstood rigorous scientific testing standards.

"Instead of taking it on faith, [Pollak] decided to examine whether the claims of fingerprint examiners have been sufficiently tested," said Mnookin, a professor at the University of Virginia School of Law. "The testing under Daubert is supposed to be testing by the scientific community, not testing through the adversarial process in court."

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