Cold Case

Cold Case is an American police procedural television series.
The series revolved around a fictionalized Philadelphia Police Department division that specializes in investigating cold cases.
Lilly Rush, the lone female detective in the Philadelphia homicide squad who finds her calling when she's assigned to "cold cases" crimes that have never been solved. Previously, she used her instinctive understanding of the criminal mind on current murders. Now, she's interrogating witnesses whose lives and circumstances have since changed, making use of today's new science and finding fresh clues to solve cases that were previously unsolvable, all of which appeals to this smart, driven detective.