"In Cold Blood" 2

"He was getting out of the car to go after them when he heard the screams, but before he could reach the house, the girls were running towards him. His daughter shouted, 'She's dead!' and flung herself into his arms. 'It's true, Daddy! Nancy's dead!'
Susan turned on her. 'No, she isn't. And you don't you say it. Don't you dare. It's only a nosebleed. She has them all the time, terrible nosebleeds, and thatt's all it is.'
'There's too much blood. There's blood on the walls. You didn't really look.'" pg 58

At this point in the book, it becomes evident that the Clutter family has finally been murdered, after a suspenseful scene-to-scene desctription of the Clutters and two men, who are the killers, even though it is not explicitly that there's any connection between them and the Clutters throughout the book. The whole time, i had been thinking, well ok he's describing them moving towards Holcomb, but are they the killers? Why is it relevant? It is also important to note that Capote did not describe or even mention the actual killings at all - he skipped from the family going to bed and the two men pulling up to their house, to the next morning in this passage where Nancy is found dead. I think the purpose of this is to leave the reader to wander what happened, why, and how, and give you alot of room for imagination, enhancing the overall reading experience.

Questions:
Why skip the murder scene?
Why did Perry and Dick (the two guys) murder them? what is the motive?
Why are they already dead and i still have most of the book left to read?