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Jack Ruby
Jack Leon Ruby (born Jacob Leon Rubenstein; April 25, 1911 – January 3, 1967) was an American nightclub owner and alleged associate of the Chicago Outfit, who murdered Lee Harvey Oswald on November 24, 1963, two days after Oswald was accused of the assassination of President John F. Kennedy. A Dallas jury found Ruby guilty of murdering Oswald and sentenced him to death. Ruby's conviction was later appealed, and he was to be granted a new trial; however, he became ill in prison and died of a pulmonary embolism from lung cancer on January 3, 1967.
In September 1964, the Warren Commission concluded that Ruby acted alone in killing Oswald, shooting him on impulse, and out of grief over Kennedy's assassination. These findings were challenged by various critics who suggest that Ruby was involved with major figures in organized crime and that he was acting as part of an overall plot surrounding the assassination of Kennedy.
Source: Wikipedia