Jack Ruby
In his book, "Contract on America", David Scheim provided evidence that Mafia leaders Carlos Marcello, Santo Trafficante, Jr., and Jimmy Hoffa ordered the assassination of President Kennedy. Scheim cited in particular a 25-fold increase in the number of out-of-state telephone calls from Jack Ruby to associates of these crime bosses in the months before the assassination, and to an attempted confession by Jack Ruby while in prison. David E. Kaiser has also suggested mob involvement in his book, "The Road to Dallas".