Eyewitnesses: The Most Common Cause of Wrongful Convictions
Eyewitnesses have always been considered very strong evidence in a criminal case. If a man robs a gas station, and the clerk identifies the defendant as the the robber you would be inclined to believe the eyewitness right? Well, it turns out that people give each others memories much more trust than they actually deserve. In a study by the University of Nebraska students were shown a staged crime. A week later the students were shown a photograph lineup, and an actual lineup. When identifying the criminal in photos the students chose an innocent person 20% of the time. With a lineup, an innocent person was identified 8% of the time. The criminal justice system treats eyewitness accounts as one of the hardest types of evidence in court, and it is used extremely often. Eyewitnesses are much less reliable than we believe they are, and this is why.
An eyewitness' confidence may seem like an important tool in determining the validity of their judgment, but it's actually not. If an eyewitness is on the stand in a trial yelling "I saw him with my own two eyes!" you may be more inclined to believe the witness. In a 1995 study comparing eyewitnesses' accuracy and eyewitnesses' confidence, the researchers found that extremely confident witnesses had only slightly higher accuracy than witnesses who had little confidence. This could be the result of witnesses' confidence being altered by other factors like emotions. These finding need to be taken into account in the court of law because if an eyewitness fervently identifies a defendant, the jury could mistakenly give more credence to the witness' identification.
Reconstruction and Social Pressures
There are two main psychological practices that lead to incorrect eyewitness accounts. Reconstruction is the process of new information reconstructing or altering memories subconsciously. For example if an eyewitness sees the defendant during the trial the eyewitnesses description of the perpetrator might be reconstructed to more closely fit the physical attributes of the defendant. Social Pressures are very powerful and can call into question an eyewitness' validity. For example, let's say a mailman witnessed a murder of a husband. He might be socially pressured by the victim's family to 'get a conviction' and alter his actual account. One of the worst things that can happen to a witness is a judgement on the defendant, such as guilty or not guilty. This can lead to changes in the witness' account to favor the witness' preconceptions, an attempt by the witness to alter the outcome of the case regardless of the lack or presence of evidence.
Cognitively there are many things that can distort, or replace memories. Interference can take place, in which chaotic or emotionally strenuous circumstances flood the brain with stimuli making details difficult to recall. Retroactive interference is when new information takes the place of old information making the old information inaccessible. For example if you memorized a phone number and then read a page of phone numbers in a phone book you would have a difficult time remembering the phone number.
Police sometimes employ both mug shot arrays and lineups. After the witness looks through the lineup and is unable to identify a suspect the witness is then shown a series of photographs. Since the only person that is in both the lineup and the mug shot array is the defendant the witness might say that the suspect looks "familiar" during the mug shot array. What the witness doesn't know is that they remembered the face from the lineup and not from the actual event. Another common problem is the power of suggestion. False memories, or distorted memories can be implanted into a witness through suggestive interrogation, carefully asked questions that can lead witnesses to alter their memories subconsciously. Mistakes are easy to make, and almost impossible to undo. Once a witness has been spoiled in one way or another their validity is gone.