with carmen prestie about those two chimps, charlie and kiko, many years ago. him to consider putting them in a social situation where they could be in the company of other chimps. he chose not to do so. i imagine that we'll be hearing more about that in the future. >> when you know what chimps are like in nature you'll understand what they're capable of. chimps on the edge features harvard anthropologist richard wrangham who studied chimpanzees in the wild for decades. he says that like humans at war, male chimps violently assert dominance through lethal raiding. >> many of the attacks happen without anybody seeing them. the body is stretched out and legs akimbo so the victim is being held out almost like a crucifixion. >> april and clay know that no matter how close you are to chimps, their violent tendencies like just below the surface. >> we hear time and time again the same refrain from former owners. if only i had known, i'd never ever would have done this. >> this is vicki mabry for "nightline" in nicholasville, kentucky. >> and explorer's "chimps on the