oke it's a long story so listen up.
Sasuke tried to kill orochimaru, then orochimaru "toke" sasuke to his other dimension world where he goes to when he's doing soul-transportation jutsu (or something like that). Orochimaru thinks he's the boss there but sasuke turns it into his world cause he has the sharingan, then sasuke thinks he killed orochimaru by jusing his own dimension against him.
But later on when sasuke battles with itachi, orochimaru appears again because he had put a little of himself into sasuke (the curse mark). Sasuke isn't able to control him en orochimaru tries to break free, then itachi suddenly uses a sword that can absorb things (or something like that xD) and absordbs orochimaru.
In the end the only thing what remains is a little white snake that tries to "run" away but gets killed by fire (I believe that was itachi's too)
So you could say that sasuke killed his body and Itachi killed his soul/spirrit.
I hope I explained it so you could understand it xD
