III- answer part 3

Trying to make Dick admit that he couldn't actually go through with the killings, Perry himself took up the knife, meaning "to call his bluff," but was seized by sudden emotion, and to his surprise found himself slitting Mr. Clutter's throat. The subsequent shootings all happened in a blind frenzy on the part of the killers, after which they fled the scene.

Here is a quote from the text,

The barrel of the shotgun roared three more times that night. Kenyon. Nancy. Bonnie. "I made Hickock do the shooting on Nancy and her mother; I told him I'd had enough."