dr. itiel dror, a cognitive neuroscientist based in london, is one of the world's leading authorities on fingerprint analysis. he says that examiners can be influenced by bias. >> we're talking about bias that's unconscious? >> absolutely. >> we're not talking about a conscious conspiracy to match up the suspect with the fingerprint. >> absolutely, we're talking about dedicated, hard-working, honest, competent forensic examiners. >> bergman: dr. dror says this is cognitive bias. and in a study to show how strong that bias can be, he took real cases-- where examiners had found a match-- changed the descriptions of the crime and then asked the same examiners to analyze them again. >> i gave the same prints to the same examiner without their knowledge, and a large majority of the examiners said now it's not a match. >> so, in over half the cases, they would disagree with their former opinion? >> yes, it changed their perception and judgment, and over half said it is not a match. >> in the study that dr. dror did, the examiners changed their mind. over half of them. >> four out of five. >> s