An eyewitness is someone who directly witnesses a crime through one or more of his or her senses. Despite the ocular emphasis of the term, an eyewitness does not necessarily have to be someone who visually witnessed the crime, but could be someone who heard the event or used other senses to be directly aware of the occurrence. In this way, a blind witness who heard the voice of a perpetrator of a crime may be more valuable than a sighted witness who saw a crime performed by people wearing masks. An eyewitness is usually considered a valuable asset for police officers attempting to solve a crime and for prosecutors looking to convict those who have already been arrested.
The report of an eyewitness can often help police officers establish potential suspects or better understand a crime scene. This sort of witness can often be brought in to help identify apprehended suspects in a police lineup or to look through books of photographs of previous offenders who resemble the description given by the witness. An eyewitness can also be used to create an image of a suspect through the use of a police sketch artist who creates a picture of the suspect based on a description by the witness.
While a single eyewitness can provide important and helpful details or descriptions to investigators, having multiple witnesses can often provide a better and truer understanding of what happened. Multiple, separate statements can be taken by police officers and compared for similar or disparate details in the witnesses' accounts of the crime. This is especially helpful when the event may have been particularly traumatic or intense, and accurate recollection of the crime can be more difficult for a witness.
Such flaws in eyewitness testimony are one of the strongest arguments against too much emphasis being placed on the reports given by witnesses. Though the reports may seem initially helpful, people are not perfect factual recorders of events. Memories can be distorted or flawed, people can lie out of a sense of maliciousness or ignorance, and other factors can influence the perceptions of a person regarding an event. Psychological studies of eyewitness reliability have shown that things like weapon focus, where a person is threatened by a weapon and details other than the weapon itself are not as clearly remembered, can adversely affect a person’s ability to recall information. Too much reliance on the memory of an eyewitness has sometimes led to misidentified suspects and innocent people being charged with or convicted of a crime.