Snape is innocent. I keep telling people this and they look at my as if I'm slightly weird. Only slightly, I think to myself, little do they know about my obsession with mashed potato. But that's another story.
I love the Harry Potter books. I particularly love the character of Severus Snape. He is a wizarding genius, with black eyes, a mordant wit and a flair for poetry. Be still my beating heart!

I am utterly convinced that in the Half-Blood Prince, he and Dumbledore arranged that Snape would end DD's life if it was for the greater good of the order. There are lots of reasons why I think this but here are some of the principal ones.
We overhear them talking, during which Snape is reluctant to do something but DD forces the issue. My own view is that DD has planned a series of information leaks about his supposed old age catching up with him ie you note that in Spinner's End, Snape tells Bellatrix that DD was seriously injured not long before ; I think this is mentioned to her because she's bound to repeat it to Voldy. After all, a great wizard like DD would be able to conjure himself a new hand, wouldn't he ? If Voldy can do it for Worntail.........In my view, that was a calculated release of information made to make Voldy think that DD was already on his last legs so that his being killed in the end seemed less surprising. It also fits in with my theory that DD isn't really dead in any event, but just wants everyone to think he is.
We note that DD wants only Snape as he and Harry return to Hogwarts and see the Dark Mark above the tower (not the other members of the Order who could have added to their numbers).
His pleading with Snape on the tower can be read as him reminding Snape to follow their pre-arranged plan - without which Snape would have been revealed to the other death eaters as on DD's side, and would have at the same time broken his Unbreakable Vow to save Draco. I think Snape was having a moment of crisis at this point and might have refused to "kill" DD if he hadn't been pressured to do it.
The Avada Kedavra curse Snape uses is different from all other descriptions of it in the books ; DD is lifted off his feet, curves gracefully in the air and falls off the tower. Yet at the point it is carried out, Harry is still subject to DD's spell, making him invisible and immobile. If the spell-caster has died instantly, his spell would be lifted, no ?
Also, the emphasis on non-verbal spells throughout the book isn't there for nothing ; I think there is a reasonable chance that Snaper/DD performed a non-verbal on DD, which make the following avada kedavra curse invalid.
As Snape flees, he orders a death eater not to perform the Crucio curse on Harry and bizarrely, gives Harry advice on how to defeat Voldy as he runs away ; peculiar actions for a supposed death eater. If Snape really was on Voldy's side, and had killed DD, wouldn't that have been the perfect moment to capture Harry and hand him over ? Or to kill him? After all, Voldy doesn't need Harry alive anymore does he ? And Voldy doesn't know about the prophecy and it's suggestion that one of them has to kill the other.
Have I convinced you ? No ? Huh ? :-3
Well, if anyone's wondering if I've given too much thought to this, they're absolutely right
