Eyewitness gear

Eyewitness testimony is generally presumed to be more reliable than circumstantial evidence. Studies have shown, however, that individual, separate witness testimony is often flawed, and parts of it can be meaningless. This can occur because of flaws in Eyewitness identification , or because a witness is lying. If several people witness a crime, it is probative to look for similarities in their collective descriptions to substantiate the facts of an event, keeping in mind the contrasts between individual descriptions.

Police lineups, where the eyewitness picks out a suspect from a group of people in the police station, are often grossly suggestive, and give the false impression that the witness remembered the suspect. In another study, students watched a staged crime. An hour later they looked through photos. A week later they were asked to pick the suspect out of lineups. 8% of the people in the lineups were mistakenly identified as criminals. 20% of the innocent people whose photographs were included were mistakenly identified.

Weapon focus effects in which the presence of a weapon impairs memory for surrounding details is also an issue.

Another study looked at sixty-five cases of "erroneous criminal convictions of innocent people." In 45% of the cases, eyewitness mistakes were responsible.