There are at least two reasons for which eyewitness testimony is important to investigators. One has to do with the process of investigation while the other has to do with winning the case in court.
Eyewitness testimony can be important during the process of investigation. It can be important because it can provide important information to the investigators. A person who can describe a suspect can be important in allowing the police to know what sort of person to look for. A person who can give a license plate number can also help in a similar way. An eyewitness account can help investigators to understand why the crime scene looks as it does. All of these things can help with the investigative process.
Once the case gets to court, eyewitnesses can be very important. Even though eyewitness testimony is not necessarily reliable, juries tend to think that it is reliable. They are likely to be much more convinced by the testimony of a good eyewitness than by more physical, but circumstantial, evidence. Thus, having an eyewitness who comes across as credible and believable while on the stand is a very good way to improve one’s chances of getting a conviction.
For these reasons, eyewitness testimony can be very important.