Fun fact: 2 Chicago mafia family members were supposed to testify about Kennedy assasination in front of US senate, guess what happened to them, they died "mysteriously".

On June 24 and September 22, 1975, Roselli testified before the 1975 U.S. Senate Select Committee on Intelligence (SSCIA) led by Idaho Senator Frank Church about the CIA plan to kill Castro, Operation Mongoose. Shortly before Roselli testified, an unknown person shot and killed Giancana in the basement of his Illinois home. This happened just days before Giancana was to testify before the committee. Giancana's murder supposedly prompted Roselli to permanently leave Los Angeles and Las Vegas for Miami, Florida.

On April 23, 1976, Roselli was called before the committee to testify about a conspiracy to kill President Kennedy.[3] Three months after his first round of testimony on the Kennedy assassination, the Committee wanted to recall Roselli. However, at this point, he had been missing since July 28.[13] On August 3, Senator Howard Baker, a member of the new SSCIA, requested that the FBI investigate Roselli's disappearance.[3]

https://en.wikipedia.org/wiki/John_Roselli