New York ? As notorious mobster John Gotti went to trial for murder and racketeering, federal investigators grilled scores of suspects about secret details surrounding the Gambino crime family boss’ precision murder plot against his predecessor, “Big Paul” Castellano.

They were looking for a mole, not a Mafioso.

The nearly 200 people questioned were all in law enforcement, many of them FBI agents stationed from New Jersey to California. The investigation — sparked by a single phone call from an irate federal judge — sought the source of a story leaked to a New York newspaper six years after the Manhattan mob rubout.

The FBI fared better with Gotti than with its internal probe. While Gotti went away for life, “no one was identified as being the source of the leaks,” a long-buried FBI memorandum concluded 13 months after the February 1992 hunt for the leaker began.

The depth and breadth of the investigation were revealed in nearly 300 pages of FBI documents released to The Associated Press via a Freedom of Information Act request.

The probe was sparked by U.S. District Judge I. Leo Glasser’s call to then-FBI head William Sessions, the documents show.

The paperwork reflects the intensity surrounding the 1992 prosecution of Gotti. Glasser imposed gag orders on everyone involved in the case.

However, the edicts failed to prevent a Jan. 28, 1992, story in the Daily News detailing how turncoat witness Sammy “The Bull” Gravano and Gotti were parked one block from the scene of Castellano’s December 1985 murder. Gravano had testified about the killing barely a month later.

The probe was declared dead in March 1993 — 11 months after Gotti’s conviction and nine years before he died in prison.