"I do not know who might be responsible for the crimes you have mentioned, kotenok," he said.  "But if I were you, I should start with Macnair and Rowle.  Neither of them has been imprisoned here, as far as I can tell, and they both like to kill for pleasure.  If anyone would be killing on their own, without authorization, I should start with them.  I presume you do not suspect Greyback."