Author's Response: What better trophy for Voldemort than to make the Heir of Gryffindor his horcrux? The Avada Kedavra was part of the attempt, but since no one had ever used a living being to make a Horcrux, it had an unexpected effect, the backfire if you will that blasted Voldy. The effect of it in Harry is all over the books: Parseltongue, their connection, etc. It didn't make him evil, but it did connect them. I think that is supported in canon. Maybe Voldy figured if he killed Harry personally, he could reclaim that bit of his soul... that's the weakest point there, but remember that many times Voldy prohibits anyone else from killing Harry... this could explain why.