Study Of Faulty Fingerprints Debunks Forensic Science 'Zero Error' Claim

Cole’s study is the first to analyze all publiclyknown mistaken fingerprint matches. In analyzing these cases of faultymatches dating from 1920, Cole suggests that the 22 exposed incidents,including eight since 1999, are merely the tip of the iceberg. Despitethe publicly acknowledged cases of error, fingerprint examiners havelong held that fingerprint identification is “infallible,” andtestified in court that their error rate for matching fingerprints iszero.

“Rather than blindly insisting there is zero error infingerprint matching, we should acknowledge the obvious, study theerrors openly and find constructive ways to prevent faulty evidencefrom being used to convict innocent people,” said Cole, an assistantprofessor of criminology, law and society.

The study appears in the current issue of the Journal of Criminal Law & Criminology.

Cole’sdata set represents a small portion of actual fingerprint errorsbecause it includes only those publicly exposed cases of mistakenmatches. The majority of the cases discussed in this study werediscovered only through extremely fortuitous circumstances, such as apost-conviction DNA test, the intervention of foreign police and even adeadly lab accident that led to the re-evaluation of evidence.

Onehighly publicized example is that of Brandon Mayfield, the Portlandlawyer who was arrested and held for two weeks as a suspect in theMadrid train bombings in 2004. FBI investigators matched prints at thescene to Mayfield, and an independent examiner verified the match. ButSpanish National Police examiners insisted the prints did not matchMayfield and eventually identified another man who matched the prints.The FBI acknowledged the error and Mayfield was released.

Wrongfulconvictions on the basis of faulty evidence are supposed to beprevented by four safeguards: having print identifications “verified”by additional examiners; ensuring the examiners are competent;requiring a high number of matching points in the ridges beforedeclaring the print a match; and having independent experts examine theprints on behalf of the defendant. However, each of these safeguardsfailed in cases Cole studied. In fact, in four of the cases,independent experts verified the faulty matches.

Despite printexaminers’ zero-mistake claim, Cole points out that proficiency testsconducted since 1983 show an aggregate error rate of 0.8 percent.Though that may seem small, when multiplied by the large number ofcases U.S. crime laboratories processed in 2002, it suggests therecould be as many as 1,900 mistaken fingerprint matches made that yearalone.

“While we don’t know how many fingerprint errors arecaught in the lab and then swept under the rug – or, worse, how manyhave still not been caught and may have resulted in a wrongfulconviction – we clearly need a full evaluation of the errors,” Colesaid. “The argument that fingerprints are infallible evidence is simplyunacceptable.”