I had never heard anything about this, and found it an interesting read.
From the "War" section of the wiki article (I removed reference numbers for easier reading):
First blood was drawn by the Kasakela community on January 7, 1974, when a party of six adult Kasakela males consisting of Humphrey, Figan, Jomeo, Sherry, Evered, and Rodolf ambushed the isolated Kahama male Godi while he was feeding on a tree. The Kasakela males were accompanied by one female, Gigi, who "charged back and forth around the melee". Despite Godi's attempt to flee, the attackers seized him, threw him on the ground and beat him until he stopped moving. Afterwards, the victorious chimpanzees celebrated boisterously, throwing and dragging branches with hoots and screams, and retreated. Once the Kasakela group had left, Godi stood up again, but probably died of his injuries soon after. This was the first time that any of the chimpanzees had been seen to deliberately attempt to kill a fellow male chimpanzee.