What is person lineups?

A "lineup" is a group of five or six people, one of which is the likely perpatrator, who are paraded onto a well-lit stage screened from the audience watching them. Most of the people in the lineup are ordinary people with airtight alibis (building employees) or other police officers in plainclothes. They cannot see the people viewing them. One or more of those viewers is the witness to a crime, or the victim of a crime. If they select the alleged perpetrator as the criminal, that weighs heavily on whether or not that person will be arrested ("eyewitness identity"). If they pick an anonymous person, the alleged perpetrator is off the hook. It's effective enough of the time that police departments continue to use it regularly.