-- Dumbledore's last words
Lured to the Astronomy Tower by the Dark Mark above it upon his and Harry’s return from the sea cave, Dumbledore encounters Draco Malfoy. Dumbledore immobilizes Harry, who is hidden under his invisibility cloak. Draco says he will kills Dumbledore, but keeps stalling. Draco and Dumbledore discuss Draco’s efforts to assassinate the headmaster and to get Death Eaters into the castle until other Death Eaters join Draco at the top of the tower. Finally, Snape appears and does what Draco has been too afraid to do. The killing curse knocks Dumbledore over the battlements, and his body falls.
The date of Dumbledore's death is deduced from the fact that Scrimgeour waited until July 31 to give Harry, Ron, and Hermione the items left to them in Dumbledore's will -- which allowed the Ministry to examine them for 30 days as allowed by Wizarding law (DH7).
In telling Dumbledore about using the vanishing cabinets in the Room of Requirement and Borgin and Burke's to bring Death Eaters to the castle, Draco states that Montague claimed to have been "trapped in limbo" while stuck in the Hogwarts cabinet before it was repaired. This seems inconsequential at the time and might not have been meant literally, but it is interesting in light of the fact that it is in limbo that Harry next - and last - sees Dumbledore. (DH35) -BB
Draco finds it surprising that someone would insist upon not using the word "mudblood" in front of them when they are about to be murdered. Perhaps this can be read on the context of Sirius' claim that the measure of a person is in how they treat their inferiors. (GF27)
Before being killed, Dumbledore puts an emphasis on manners and uses them to irritate people who are hostile to him. This is in the third-from-last chapter in the book. Dumbledore did the same thing on Privet Drive in the third chapter into the book. -BB
Amycus Carrow says Dumbledore has always been characterized by "talking and doing nothing." The irony is that that is exactly what Draco is doing in that instant. -BB
In another instance of Professor Trelawney being right all along, Dumbledore's death is consistent with her drawing "The Tower" from her tarot cards and using it to predict an imminent tragedy. (HBP25) -BB