In many criminal cases, the police rely on the testimony of an eyewitness to the crime. Eyewitnesses may have crucial information about what happened, of course. They are also frequently used to identify a suspect. These identifications are typically done by having the eyewitness look at a lineup or an array of photographs.
However, there is overwhelming evidence that eyewitnesses are often wrong. Memory is much more fluid than you might imagine, and witnesses can be mistaken or even led to the wrong conclusion despite feeling quite confident in their identification.
Over the years, experts have developed what are called "pristine conditions" for lineups and photo arrays in order to minimize these influences on the witness:
- The lineup or photo array is conducted by an officer who does not know which person is the suspect
- The lineup or photo array contains only one suspect
- The people chosen should resemble the description of the suspect, and the actual suspect should not stand out in any way from the group
- The witness should be told that the suspect might not be in the lineup or photo array
- The witness's confidence in their identification, if any, should be measured immediately after the identification -- before any communication between the officer and the witness
Unfortunately, identifications are not always performed in pristine conditions. Far too often, lineups and photo arrays are used not as neutral fact-finding tools but as a way to confirm the officer's opinion about the suspect, and police can manipulate the lineup or array to be extremely suggestive to the witness.
Recently, some high-profile researchers in this area analyzed the data from a number of studies on whether there is a way to predict which eyewitnesses are accurate and which are mistaken. They concluded that the more confident an eyewitness is in their identification, the more likely that identification is accurate.
That's very interesting, except that we know that many eyewitnesses have been shown to be wrong despite high levels of confidence.
Critics of the theory that greater witness confidence promises greater accuracy have pointed out one major issue with it. It assumes that the identification took place in pristine conditions. In other words, the degree of an eyewitness's confidence tracks with accuracy only when the witness was not led to their conclusion by suggestive conditions in the lineup or array.
The lack of pristine conditions in many eyewitness IDs helps explain why eyewitness testimony, while compelling, is often wrong.