I used to think that the HBP was an assassin the Voldy was going to hire to kill Harry. But then I realised that Voldy would only take away from the respect he's earned for himself in the wizarding community by hiring someone else to do his killing for him. So witht that I'm changing my veiw to Dumbledore. I think it's him. I want it to be him. After all we don't really know anything about Dumbledore's past. I think that anything about Dumbledore's past would be absolutely fascinating.