The FBI turned to one of the country’s most infamous former mobsters as investigators sought evidence that former bureau director James Comey intended to threaten President Donald Trump with an Instagram photograph reading “86 47,” newly filed court records show.

Agents interviewed former Gambino crime family underboss Salvatore “Sammy the Bull” Gravano in May, according to motions filed Tuesday evening by Comey’s attorneys. The unusual investigative step was part of an attempt to establish that Comey would have learned a supposedly violent meaning of “86” while prosecuting organized crime cases early in his legal career.