Interesting to me all these "experts" seem to know little about chimp behavior. Last night (I think on Discovery channel) they played "The Dark Side Of Chimpanzees." Showed how the chimps go out on silent patrols in groups. If they catch a smaller group and especially a single male, they attack in EXACTLY this way. They specifically beat and bite the victim, and the make a point of chewing off body parts. They showed two of these attacks on film. In one they killed the other chimp and bit pieces off, including the genitals. I believe this gentleman was also bit in the groin. The other chimp got away after awhile but was expected to die.
I think chimps also have another monkey species they routinely grab, and eat the brain out of.
Of course the article can't admit the chimps are just naturally aggressive especially in groups. They do this to protect their territory. As for strength, I believe they said 4 or 5 of the chimps can kill a rhino.