*SPOILERS - WHY SIRIUS WANTED TO KILL HARRY - *SPOILERS*

Actually, Sirius did not want to kill Harry. Everything was set up to make us believe Sirius was after Harry, when he was really after Scabbers (Ron's rat). Everyone believed Sirius was after Harry, because they believed that Sirius was the one who told Voldemort where Lily and James were hiding, when in reality, Peter Pettigrew (Ron's rat) was the one who did so. Sirius was never after Harry.