In the United States a photo lineup is a procedure used by law enforcement to aid a witness in identifying a criminal suspect. A photo lineup typically consists of a number of photographs, including a picture of the suspect. By law, subjects in the photo lineup must be similar in appearance to the suspect so as not to unduly highlight or intentionally elicit a response that could be prejudicial to the accused. Positive identification by the witness can be used to arrest the suspect, and may come into evidence should the case go to trial.
If there is no corroborating forensic or circumstantial evidence, witness identification alone can make for a weak prosecution case and provide plenty of fodder for the defense to challenge. The court considers many factors involving the nature of positive I.D.s, witness character and relationship to the crime and suspect.
Although a multi-picture photo lineup is standard, there are instances where identification is made other ways. A single photo might be used if police have identified a suspect or person of interest and need to move quickly to protect public safety. In other instances, law enforcement might conduct a show-up. This is common when police apprehend a suspect a short distance from the crime scene, usually within minutes of the crime occurring. Police might drive one or more witnesses past the scene of the apprehension to see if witnesses can make a positive I.D. or eliminate the suspect.
When a suspect is already in custody, an in-person lineup might be used instead of a photo lineup. The in-person lineup consists of several persons including the suspect, and takes place at a police station. The witness observes the lineup from behind a one-way glass so that participants in the lineup cannot see the witness.
A photo lineup is a valuable tool in gathering evidence that can lead to an arrest. The flexibility of digital photography combined with public and private databases has made the job of law enforcement easier when it comes to constructing a photo lineup. A positive I.D., however, is only the first step in a long line of hard work that is required for the successful conviction of a guilty suspect.