By 2021, community forums (like Subscene, OpenSubtitles, and GitLab archives) had settled on a definitive standard:

A career criminal who has successfully infiltrated the Special Investigations Unit to feed info back to Costello.

The film's exploration of , identity , and corruption earned it four Academy Awards, including Best Picture and Best Director for Scorsese. Technical Context: Blu-ray and Digital Versions

: Costigan eventually discovers that Frank Costello is himself a protected FBI informant. The Murder of Queenan