well, that's exactly what happened with brandon mayfield. >> bergman: there had been other mistakes in the past, but the mayfield case highlighted the weak link in fingerprint identification: the examiner. >> running both prints through... >> bergman: unlike fingerprint analysis on television, machines do not make a match-- people do. >> the examiner is the instrument of analysis. there is no objective criteria. it's a subjective judgment of the fingerprint examiner. >> bergman: 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