John Kobler, in his excellent Capone bio, says that Big Jim, infatuated with Dale Winter, a singer in his supper club, wasn't taking care of business, ignoring Torrio's grand plan to cartelize the upcoming booze bonanza among the gangs. So, logically, Big Jim had to go; and Torrio, rather than killing his uncle, gave the contract to Capone. Both benefited. BUT: Kobler stops short--he merely says "shots rand out in the vestibule." Lawrence Bergreen, a later Capone biographer, says the killer was Frankie Yale, Capone's old mentor in Brooklyn, who did it to expand his influence in Chicago. BUT: Bergreen doesn't follow up om that--the next we hear of Yale in his book, he's still in Brooklyn.

That's the long answer. Short answer: NFI.