OK, I figured it was Snape to begin with. It was pretty obvious - the book in the bottom of a drawer and with sheer unadulterated genius in everything to do with the potion part. Although really it was pretty annoying that Harry didn't quite GET what was written in there - and was rather amusing how much he liked and admired the personality that was shown.
I was misled for a bit - thought that Draco had been bitten by Fenrir, and that it was part of the rather nasty 'recruit the kiddies' thing that the wolf creep was doing.
Also figured out, knowing that SOMEONE was going to die, that it would be Dumbledore. Though the whole thing seems to contain a touch of withering stupidity that bothers me.
Snape killing Dumbledore? Yeah. He had to. He made the Unbreakable Vow. And he was, in a perverse way, saving Draco from the Dark. And, I suspect, Dumbledore knew about it, though in his overconfidence he thought he could avoid letting things get that bad.
Too bad, really, that Harry is not likely to understand that. He's better than he was but he's still an idiot. Not that I'd expect great sophistication from a kid who was kept in a closet under the stairs. I really expect better from Snape though. He's being far too stupid in his treatment of Potter, it really continues to be inconsistent with the depth of character he's shown otherwise. If he's THAT good a legilimens, he would know precisely WHY Potter thinks the way he does, and if he had a tenth of the subtlety required to make a potion the way he went on in his first clas, then he'd ALSO know that his every action was guaranteed to make the kid hate him. Stupid for no reason.