Yes, the strongest evidence that it was not only the Mafia that were involved in killing the Kennedies is simply that the Mafia was in no position to control or affect Kennedy's secret service protection in Dallas (which was severely compromised on that day in a number of very odd ways). They were also in no position to control the Warren Commission or the FBI or the CIA. If the Mafia alone had done the job on its own, those people would have gone after the Mafia. The only way they would NOT have gone after the Mafia is if they were also in on the plot up to their eyeballs. In that case they would have covered it up, because their interests and the Mafia's would have then coincided.