<p>Based on other perspectives I've read, I've revised my opinion slightly. After much deliberation, I'm siding with [this</a> post<a href="not%20mine">/url</a>. It's very long, but it's a fascinating, as well as credible argument:</p>
<hr>
<p>First of all, R.A.B. has to be Regulus Black. This has practical implications for Harry because, when he figures it out, it will help him find the real locket Horcrux.</p>
<p>Where is the locket? On page 116 of OotP (U.S. paperback edition), Sirius and the kids are cleaning out an old cabinet which contains items such as a snuffbox with Wartcap powder, a music box, and a 'heavy locket which none of them could open'. I'd bet that's the locket in question.</p>
<p>Now, one of three things could have happened to the locket, which we assume was thrown into the bin with the other things that had been in the cabinet: either it went out with the rest of the rubbish, or Kreacher nicked it (and Harry will have to go back to Grimmauld Place to retrieve it) or Mundungus stole it and fenced it. I'm willing to bet on this last one; why else would the scene with Mundungus and the stolen Black family silver have been given such prominence in HBP, except to remind us of Mundungus' activities so that it's not a shock when JKR brings it back up in the seventh book? </p>
<p>Aside from the practical implications for getting and destroying the locket, Regulus' note sheds some interesting light on Regulus' death, Dumbledore's death and Snape's 'betrayal'. Why is this?</p>
<p>Regulus states that he knows he will be dead by the time the Dark Lord gets the note. Not because the Dark Lord or anyone else will kill him for stealing the Horcrux (Dumbledore mentions, in his conversation with Harry about Riddle's diary, that Voldemort probably doesn't automatically know when a Horcrux is destroyed); instead, I think Regulus knew that the potion in the cave would most likely kill him when he stole the Dark Lord's locket Horcrux, which changes our conception of his death. Regulus was not, as Sirius said, an idiot who joined up and then got himself killed when he saw what he was asked to do and backed out; instead he found out about some of Voldemort's most precious plans for immortality and made an active attempt to thwart them. He went out in a blaze of self-sacrificial glory.</p>
<p>Now, what does this mean for Dumbledore and Snape? Well, it gives us the knowledge (or at least the hint) that the potion in the cave is probably going to kill the drinker. Dumbledore hints at this too; he implies that, though it won't kill immediately, it will probably leave the drinker alive long enough to cause a lot of pain or perhaps even allow Voldemort to find out who had attempted to steal one of his Horcruxes. The biggest confirmation that the potion is lethal, and that Dumbledore knows or at least suspects it, is that he does not allow Harry to drink it--he all but says that he is expendable and that Harry is not. Also, later, there is the fact that Dumbledore chooses to save Harry (well, save him from himself, really, by Freezing him so he can't do anything rash on the tower) instead of defending himself; defending himself is less important because he knows is going to die anyway.</p>
<p>So Dumbledore knows he is dying during the scenes after retrieving the locket, during the return to Hogsmeade and on top of the tower. Throughout the conversation with Malfoy he grows steadily weaker. Even as he is convincing Malfoy not to kill him, he is *already dying<a href="and%20probably%20has%20known%20he%20was%20coming%20close%20to%20death%20all%20year%20anyway,%20or%20why%20would%20he%20have%20taken%20the%20trouble%20to%20pass%20his%20work%20on%20the%20Horcruxes%20on%20to%20Harry?">/i</a>. Dumbledore reasons with Malfoy, not to save his own life but to spare Malfoy having blood and murder on his hands. The fact that Dumbledore is dying anyway would not make Malfoy's act of murder any less despicable, and Dumbledore does not want Malfoy to become a murderer; we get the impression that Malfoy is not naturally evil, anyway, in this scene. He is under extreme coercion.</p>
<p>Things change a bit when the Death Eaters arrive--now there is the new problem of keeping Malfoy alive. Dumbledore knows that, if Malfoy doesn't kill him, Malfoy will probably either be killed on the spot by the Death Eaters or taken to Voldemort, who will kill him. </p>
<p>So, here's my theory: when Snape appears, Dumbledore knows this is the perfect opportunity to accomplish all of his immediate goals--save Malfoy's life and keep him from doing a despicable act, plus allow Snape to fulfill his Unbreakable Vow (which I am sure he knew all about, just as he knew all about Malfoy's plan) and therefore a) not die and b) remain 'in' with the Death Eaters as a spy--and all this simply by doing something he knew he was going to do anyway: die.</p>
<p>However, we are stuck in Harry's POV, so all we see is Dumbledore apparently pleading with Severus for his life, then Snape 'gazing at the professor for a moment' with a 'look of hatred and revulsion' and finally casting the Killing Curse. Later Harry will report this to his friends and members of the Order and it will be seen as a great betrayal (by everyone except Harry, who has 'known' it all along).</p>
<p>But back up a moment: Snape gazes at the Headmaster for a moment. Two accomplished Legilimens do nothing but look at each other for a moment in the midst of a heated battle situation, and we are to assume there is nothing passing between them? Oh, no. I think Dumbledore is asking Snape, via his thoughts, to kill him. Remember that Dumbledore's pain and delirium in the cave have already led him to ask for release by death ('Kill me,' he says to Harry). Now Dumbledore is a bit more rational, but he sees that his own death at Severus' hands can serve a purpose. His pleas are not for his life but for his death.</p>
<p>Snape does it without question or argument, just as he went back to Voldemort at Dumbledore's behest after the Tri-Wizard tournament. Unlike Harry, Snape takes Dumbledore's word as law.</p>
<p>Reinterpreted in light of a request by Dumbledore, Snape's look of 'hatred and revulsion' takes on a new meaning. This is not hatred and revulsion for Dumbledore personally (or what Dumbledore stands for) so much as hatred and revulsion for being asked to do this to Dumbledore, for being asked to add murder to all of the other things he has done. This may explain also Snape's extreme reaction, later, to being called a coward; he has just been asked to kill the man in whom he placed his trust--the man who has protected him for fifteen years, and for whom he has done dangerous things, including spying and now committing murder in order to keep a student safe and uncorrupted by evil--and has complied with the request. Of course being called a coward after all this, and by Potter, would rankle. </p>
<p>[/lecture]</p>
<p>The locket/Regulus connection is very close to a sure thing--we know that JKR likes to plant clues for us, and a magically-sealed locket just happening to be in a house once occupied by a person with the initials R.B. (though we don't know about his middle initial) can't be a coincidence. The Snape thing, on the other hand, is much more my interpretation, though I do think the facts support, or at least allow for, it. When I've had a bit more sleep I'll go look up the exact quotes and page numbers...not to mention go back through 'Spinner's End', and see if that sheds any more light on the situation.</p>
<hr>
<p>-- <a href="http://www.livejournal.com/users/garlandgraves/3409.html%5B/url%5D">http://www.livejournal.com/users/garlandgraves/3409.html](<a href="http://www.livejournal.com/users/garlandgraves/3409.html%22%5Dthis">http://www.livejournal.com/users/garlandgraves/3409.html)</a></p>
<p>Again, I recommend the post I linked in my first comment for more in-depth analysis of Dumbledore's actions.</p>