The problem with Ruby as Mafia hit man for Oswald is that it you have to believe that this loudmouth, braggart, no-account strip club operator would be trusted by the Mafia to be part of the crime of the century. Apart from that, Ruby's movements on 11/24/63 are far too random for him to have been part of a conspiracy. Consider this timeline--verified by phone records, video and eyewitness testimony:

10 a.m.: Oswald was scheduled to be moved from Dallas Police HQ to the Dallas County jail. At 10 a.m, Ruby was at home, on the phone, sobbing about how badly he felt for Jackie and her kids.

11 a.m.: Oswald wasn't moved at 10. At the last minute, a postal inspector asked for and received permission to interview Oswald about his mail-order purchase of guns. The interview took about an hour. At 11 a.m., Ruby was driving toward a Western Union office 1.5 blocks from police HQ.

11:07 a.m.: Oswald still wasn't moved. He requested a sweater because the weather had turned colder. At 11:07, Ruby's car was parked outside the Western Union office, with his favorite dog inside.

11:10 a.m.: The van that was to take Oswald to the County Jail was too tall to clear the ramp to the garage of Police HQ. Captain Will Fritz decided to use the van as a decoy, and to move Oswald in an unmarked car. At 11:10, Ruby was inside the Western Union office, waiting to wire $20 to a stripper who needed help with rent and food.

11:17 a.m.: The lone policeman guarding the ramp to the basement of Police HQ stepped into the street to direct traffic away from the ramp so the unmarked car could be backed down. At 11:17, Ruby walked from the Western Union office and down the unguarded ramp, mingling with reporters and camera crews.

11:20 a.m.: Oswald was taken down to the elevator lobby in the basement to wait for the unmarked car that would take him to the County Jail.

11:25 a.m.: Police car impeded by crowd of reporters. Oswald moved forward – Ruby moved in and shot him, was wrestled to the ground. If the unmarked car had been where it was supposed to be when Oswald was moved forward, Ruby would have been blocked, and he wouldn't have been able to shoot Oswald.

Bottom line: Ruby may have been motivated to kill Oswald because of his personal feelings, and may have come to Police HQ to kill him. But his movements on that morning were far too random to be part of a conspiracy. It was a crime of opportunity, not part of a conspiracy.