"Person of interest" is a term used by law enforcement in the United States, Canada, and other countries when identifying someone possibly involved in a criminal investigation who has not been arrested or formally accused of a crime. It has no legal meaning, but refers to someone in whom the police and/or domestic intelligence services are "interested", either because the person is cooperating with the investigation, may have information that would assist the investigation, or possesses certain characteristics that merit further attention.
While terms such as suspect, target, and material witness have clear and sometimes formal definitions, person of interest remains undefined by the U.S. Department of Justice.
History
This phrase was first utilized by law enforcement in 1986, during the investigation of the Green River Killer. It was coined by Fae Brooks, a member of the King County Sheriff's Department at the time of the investigation.
According to Eric Lichtbau in The New York Times: