stoolie
/ˈstuli/
noun
- A person who gives information to the police or other authorities about the illegal activities of others; an informer.
- The gang suspected there was a stoolie in their group who had talked to the FBI.
- No one trusted him after they found out he was a stoolie for the police.
- In crime movies, the stoolie is often the character who gets caught and turns on his partners.