Originally posted by zombieman
I think Dumbledore instructed Snape to kill him, in the tower after he had drunk the potion he asks Harry to fetch Snape. I think Dumbledore wanted Snape to kill him to save Draco Malfoy, Dumbledore could see that Malfoy was innocent and didn't want to become a killer. I think Dumbledore knew his time was up soon anyway, and when he heard how Voldemort was using Malfoy, he instructed Snape to make the unbreakable bond.
good point...maybe when Dumbledore was pleading with snape saying, "serveus....please" he was pleading with him to kill him