Having someone witness a crime may seem like it creates an open and shut case. Most people assume an eyewitness testimony is a solid proof of what occurred.
However, research has shown over and over that eyewitnesses are largely unreliable. The testimony of a person who saw a crime occurs is not enough to prove guilt beyond a reasonable doubt due to the infallible nature of this type of evidence.
Memory is tricky
The human mind is not always perfect. Memory issues can distort an eyewitness account of an incident. If you cannot remember something, your mind may fill in the blanks using other information. So, it is highly likely that you may suffer from the influence of information you have heard about the incident to create a memory that is not completely valid.
Perception is key
When multiple people witness an incident, there are very good chances each will have something unique to add to the narrative. Sometimes, two people could see the same thing happen and have completely different accounts of what happened. The reason is that every person has different perceptions of events.
Trauma can cloud the mind
If the incident was especially traumatic for a witness, it could alter how he or she remembers what happened. Trauma can cloud the mind and distort memories. It could block out important parts of what the person saw, making him or her an unreliable witness.
Eyewitnesses may seem like they are excellent sources of evidence, but the faults in the human mind can make them the opposite.