It was a grisly sight: a murdered chimpanzee, his body beaten, bloodied—and partially cannibalized—by members of his former social group.

Researchers who found the gruesome scene in Senegal in 2013 knew that chimpanzees are no strangers to lethal violence. At every chimpanzee site that’s been studied for more than a decade, scientists have observed conflicts that end in death.

But killing within a community is rare.

The incident—described recently in the International Journal of Primatology and whose aftermath was caught on video—is just the ninth recorded case of a chimpanzee community killing one of its own.

“It was incredibly hard to watch,” says study co-author Jill Pruetz, an Iowa State University anthropologist and National Geographic Society grantee. “I