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 was really disturbed for about three days [afterward], as if you had a falling-out with a friend.”

Back in 2007, Foudouko was the leader of more than 30 western chimpanzees (Pan troglodytes verus) living in Fongoli, a 10-square-mile patch of savanna in southeastern Senegal. (Read more about Fongoli chimps in National Geographic magazine.)

But a rebellion against his rule banished him to Fongoli’s outskirts—the start of a five-year exile that ended with his death at the hands of his former underlings, a killing perhaps motivated by competition over mates.

“Killing enemies is pretty easy to explain, but killing your friends is a puzzle… There’s this really interesting tension between cooperation and conflict,” says Michael Wilson, a University of Minnesota anthropologist who studies chimpanzee aggression. He wasn’t involved with the study.

“It makes me think of The Sopranos.”

Primate Politics

Since 2005, Pruetz and her colleagues have painstakingly studied the chimps of Fongoli, one of the few sites in western Africa where the apes have grown fully accustomed to human researchers. (Read more about Fongoli’s chimpanzees, which have been observed using sticks as spears.)

Pruetz’s observations have revealed a daily life full of politicking. Chimpanzee communities are led by “alpha males” and coalitions of male allies, flanked by females and the young. While females strike out for new groups after reaching sexual maturity, males stay in their birth communities, jockeying for social dominance with displays and shifting alliances. “It’s a bit like a soap opera,” says Pruetz.

View Images Adult male chimpanzee Mike (left) and adolescent male LX (right) examine Foudouko's body. Photograph courtesy Jill Pruetz

In early 2005, Pruetz and her team identified Foudouko as the alpha male—the one male to which all others pant-grunted, a sign of submission. His furrowed brow and imperious air led one research assistant to nickname him Saddam, after the Iraqi dictator Saddam Hussein.

But in September 2007, Foudouko lost his grip on power, after his second-in-command—a male named Mamadou—was hobbled by a grievous leg injury. Mamadou’s fall from grace left Foudouko exposed, letting a group of younger males run him out of Fongoli in March 2008. After he disappeared, Pruetz and her colleagues thought he had died. (See intimate photos of Fongoli chimps.)

To Pruetz’s shock, Foudouko found his way back to Fongoli nine months later, a shadow of his former self. Now timid at the sight of humans, he was reduced to hiding behind trees or tufts of grass along Fongoli’s outskirts. For five long years, Foudouko would live the life of an exile, periodically ingratiating himself with the new alpha male—Mamadou’s brother David.

While Mamadou and David welcomed his return, the young males who had chafed under his rule were far less sympathetic. They regularly chased Foudouko out of the community, assailing him with strange calls the researchers did not recognize.

Scene of the Crime

Before dawn on the morning of June 15, 2013, Pruetz and her assistant Michel Sadiakho heard noises from about a half-mile away from their camp: a band of chimpanzees rapidly moving to the south from their nesting site, calling out in an uproar. Pruetz, ill with malaria, couldn’t go see the hubbub, leaving Sadiakho to run after them. (Read more about daily life in Fongoli.)

What Sadiakho saw devastated him. Foudouko, who was around 17 years old, lay there dead, his hands covered in bite marks and scratches—implying that two other chimpanzees had held him down as others beat his head and torso. A gaping wound on his foot, perhaps a bite, had peeled back much of the skin and likely led to severe blood loss.

As morning came, Pruetz and her team watched many of Fongoli’s male and female chimpanzees harass—and partially cannibalize—his body, tearing out his throat and biting at his genitals.

View Images Foudouko's body on the late morning of June 15, 2013. Photograph courtesy Jill Pruetz

Not all of the chimpanzees expressed such enmity. Mamadou, for instance, seemingly tried rouse his one-time ally by dragging him around and screaming in his face. David barely touched the corpse. But to Pruetz’s surprise, the female that most aggressively cannibalized Foudouko’s body was Farafa, Mamadou and David’s mother. “She obviously wasn’t enamored with Foudouko,” she says. “I don’t really know how to explain that.”

Pruetz and her colleagues suspect that Foudouko’s murderers could have been motivated by sex.

Sadhiako, for one, speculates that Foudouko may have approached a female chimpanzee in heat. Competition for mates is fierce in Fongoli, where males outnumber females.

A 2014 review co-authored by Pruetz, Wilson, and 28 other primatologists concluded that chimpanzees’ lethal violence most likely arose from competition for mates and resources.

“Intra-group killing looks like it’s really about reproductive competition, [with] males killing other males,” says University of Minnesota’s Wilson. “The signals of reproductive competition are really quite abundant; the killings are just an extreme point.”

Almost Human?

Chimpanzee cannibalism has been documented since the early 1970s and has featured more macabre cases, such as one where an adult female severed and ate all of a male’s genitals.

But whether his demise sheds light on violence in people, chimpanzees’ close cousins, is a matter of debate. (Also see “Chimp Gangs Kill to Expand Territory.”)

Wilson, for one, is comfortable drawing a line between chimpanzee murders and homicide—but Pruetz, much less so. “I hesitate to say something about living humans, because they’re so complex,” she says.

In fact, she says that what most struck her were the differences between chimpanzees and humans.

When the chimpanzees finally dispersed after beating Foudouko’s body, Pruetz and her colleagues buried him under supervision of Senegalese authorities.

The remaining chimpanzees seemed to comfort each other, but also struggle with understanding what had happened. Through the night, nervous calls rang out over Fongoli, in the direction of the grave.

“They were still so afraid of the body,” she says, which highlights “their lack of concept of death… and the finality of it.”

After years of analyzing the gruesome encounter, Pruetz expressed relief at finally publishing it. But as the young males’ insurrection continues, she and her team may have more exiles—and victims—to study: Foudouko’s former allies.

“Mamadou has similarly been kicked out of the group, and David is still [the alpha male], but he has been attacked several times since,” says Pruetz. “Every once in awhile, something will happen that makes me think that maybe [Mamadou] is still out there.