The Doctor never kills anyone.He is responsible for a lot of deaths.He shot either the diamond or the machine focussing the diamond to break the link the Time Lords were using to travel to Earth.
I thought that the character named The Woman,played by Claire Bloom,was the one whose identity was hinted as possibly being the Doctor's mother.According to the review in the latest DWM the answer may be revealed in the new edition of The Writer's Tale which is published later this month.Though that may just be tease.
And what about the weeping angels?Are they fallen Time Lords?