Can you rely on fingerprint evidence?

"Despite the perceived infallibility of fingerprint evidence, the study found that experts do not always make the same judgment on whether a print matches a mark at a crime scene when presented with the same evidence twice.

The finding comes in the wake of two high profile cases in which fingerprint matches were subsequently shown to be wrong. The Scottish police officer Shirley McKie was wrongly accused of having been at a murder scene in 1997 after a print supposedly matching hers was found near the body.

And in 2004 Brandon Mayfield was wrongly linked to the Madrid train bombings by FBI fingerprint experts. Fingerprint examiners say these are isolated mistakes and claim that the science of fingerprint matching is sound.

The study by Itiel Dror, a psychologist at Southampton University, suggests otherwise. "I wanted to see if it is as objective and scientific as it claims to be," he said. "I wanted to see if the same expert would make the same decision on the same fingerprint if it is presented in a different context." He presented six fingerprint experts from various countries including the UK, the US and Australia with eight marks from crime scenes (called latent prints) and eight inked marks from suspects. The experts, who had 35 years experience between them, had all given judgments on the pairs of prints in previous court cases - four as matches and four as exclusions.

But Professor Dror engineered the experiment so that none of them knew they were participating in a study, something that he says makes the study much more powerful. "If people know they are studying them they behave differently, especially if you are studying errors," he said.

Of the 48 tests, the experts changed their decision in six cases and only two of the experts were consistent with their previous decision in all of their eight cases. They were more likely to change their decision if given contextual information, such as "the suspect has confessed", that conflicted with their previous judgment.

"The same expert on the same fingerprint can make totally conflicting decisions, depending on the context," said Dr Dror, who presented his results at the British Psychological Society's annual meeting in York.

Unlike other forensic fields, such as DNA analysis, which give a statistical probability of a match, fingerprint examiners traditionally testify that the evidence constitutes either a 100% certain match or a 100% exclusion. Dr Dror said this may contribute to mistakes."

- Study questions reliability of fingerprint evidence

Via Psychology and Crime News Blog