I cannot say I'm pleased that Mr. Potter seems finally to have developed the perspicacity of which I have ever considered him incapable, but I do find it reassuring to hear that his discretion remains, as always, very nearly nonexistent. It was I. I expect it's too much to hope that he hasn't mentioned it to anyone else.
My side, then, is as follows: I killed Professor Dumbledore on his own orders. His time was already quite short, and while I don't pretend to understand all of his reasons, I believe he trusted me to do it in a less spectacular fashion than someone else might have. It also solidified my credibility, as you may have noticed, with the Dark Lord and his followers. I have always Since the Dark Lord's disappearance I have been as eager for His demise as anyone else in the Order, and have worked to accomplish it as I was directed. I was left with a final set of marching orders which require me to remain in fairly close contact with the Dark Lord, but as far as I can tell the time to execute them hasn't yet arrived. Naturally, they're to do with Mr. Potter. As they do not involve allowing him to be murdered by Death Eaters, I disguised myself as one of my colleagues here and helped him to escape. It seems I could have been more careful.
I would take it as a great personal favor if you instructed Mr. Potter to keep his mouth shut. It should not be too much to ask, as his safety depends upon it just as much as mine. If there's anything else you wish to know, I will do what I can to help you, but you will understand that Dumbledore has always been annoyingly selective in his distribution of information. I have nothing very little else that I think will be of great use, or that I think wouldn't be better kept a secret at the moment.