At a bargain rack, I found a book about Sam Giancana that his nephew wrote. According to the book, everyone involved in the assasination--Oswald, Ruby, even Tibbits [?] had Chicago connections. The story is that Joseph Kennedy had stepped on his fellow mobsters' (post-Prohibition) liquor-distribution toes. To save his life, he asked Giancana et al. to help him elect his sons to the presidency, thereby ensuring Mob control over American government. When they did help elect the Kennedy's, the patriarch, instead of protecting his friends, had Jack and Bobby use the Dept. of Justice to roll them up. Not surprisingly, the move wasn't well received. Supposedly, Sirhan Sirhan was heavily in debt to the Mob, and Sam Giancana was thinking about whacking Frank Sinatra over the Kennedy's disaster, but he liked him too much, personally.
However, if Ruby whacking Oswald wasn't proof of a mob connection, there isn't any such thing as proof.