cold case

A crime that has not been solved and is no longer the subject of an investigation due to an absence or dearth of conclusive evidence or activities of the suspect. After two years without any new leads, the murder of Georgia LaPierre has been labeled a cold case by local detectives. A number of cold cases from the late-20th century have been solved or reopened thanks to advancements in DNA testing. Don't let my mother's murder become just another cold case—her killer is out there!