Researcher Jill Pruetz and her assistant had settled into their camp in the Senegalese savanna one summer evening when they were startled by a loud ruckus in the distance. To them, the sound was unmistakable: a half-mile away, a band of chimpanzees were moving from their nesting site and calling out into the darkness.

Something had obviously disturbed them, thought Pruetz, an anthropologist at Iowa State University who had studied the group of more than 30 chimps for years. She decided to wait until morning to see what had happened.

What she found was gruesome — not to mention highly unusual. A chimp named Foudouko, a former alpha male, lay bloodied and dead under the trees. Cuts and gashes covered him, suggesting that some chimps had held him down while others beat him to death.

Pruetz and her team watched as Foudouko’s companions prodded and inspected his body. At first they seemed confused, as if waiting for him to wake up. Then they turned violent, hitting and dragging his corpse. At one point, they tore out part of his throat. The most morbid moment came when several chimps ripped pieces of his flesh and ate them.

“It was very disturbing to see the way these chimps we all know and love were treating him,” Pruetz told The Washington Post in an interview this week. “I was shocked by how brutal they were. It took me a few days to get past those feelings.”

Lethal violence among chimpanzees, while not particularly common, is well documented. But examples of a chimp community killing one of its own are few and far between, as Pruetz and her team describe in a recent article in the International Journal of Primatology. Foudouko’s death, which happened in June 2013, represents the first such case on record among West African chimps and just ninth recorded case overall, according to Pruetz’s research. (In 2014, a Scientific American article citing Pruetz said there were eight “intracommunity” killings on record.)

Pruetz suspects Foudouko may have been killed over competition for females and that the beating may have been retaliatory. His group had an imbalance of the sexes, with 13 adult males and 7 adult females.

“Usually in chimp communities that’s reversed,” she said. “This type of lethal coalitionary aggression is rare. When it does happen, it’s usually between communities.”

Foudouko’s relationship with his fellow chimps was turbulent.

As recently as 2007, Foudouko was the alpha male among his band at Fongoli, a 10-square-mile wooded plain in southeastern Senegal. Pruetz and other researchers have studied chimps there since the early 2000s, spending years “habituating” the animals to be comfortable around humans.

A dominant male chimpanzee listens to calls in Kibale National Park tropical rain forest, 354km southeast of Uganda’s capital Kampala, December 2, 2006. Researchers studying mating preferences within the Kanyawara chimpanzee community say male chimpanzees consistently prefer the oldest females in their community as mating partners. Picture taken December 2, 2006. REUTERS/James Akena (UGANDA – RTR1JZR8)

Around 2005, Pruetz told The Post, the researchers identified Foudouko as the leader of the group when they observed other males “pant-grunting” to him, showing their submission. He was probably a teenager at the time, she said, and the researchers noted that he was more aggressive than most alpha males. One of Pruetz’s assistants nicknamed him Saddam, after Saddam Hussein, the late dictator and president of Iraq, though it was more for his furrowed brow than his behavior.

Foudouko ruled over the community for at least two years, but, like Hussein, he was eventually deposed. In 2007, his lieutenant, a male named Mamadou, was severely injured. Losing the beta male caused Foudouko to run away, Pruetz said.

“That was quite astounding because chimps are such social animals,” she said. “Chimps don’t often leave their groups. They have very strong bonds within the group.”

Foudouko lived in “exile” for five years. For a time, Pruetz thought he was dead, but in 2012 he started appearing on the fringes of the group’s territory about once a month. When he would, males would often chase him away.

Not long after, he was killed — possibly because he tried to approach a female in the night, Pruetz said. The researchers captured the abuse and partial cannibalism of his dead body on video. Pruetz said the chimps seemed to think he was still alive, alarm-calling at his body, then attacking it all over again.

“They were so fearful of him still,” she said. “When I saw him I could tell right away that he was dead. But they didn’t seem to understand.”

A strikingly similar act of chimp-on-chimp violence was documented in 2011 and made public in a 2014 journal article. An alpha male near Lake Tanganyika in Tanzania had led a group for four years when he attacked the second-ranking male, as New Scientist reported. Four other chimps charged, biting and beating him until he died. Researchers, who captured the attack on video, said the other chimps may have been motivated by competition for females.

Such cases have piqued researchers’ curiosity.

“Killing enemies is pretty easy to explain, but killing your friends is a puzzle,” Michael Wilson, a University of Minnesota anthropologist who was not involved with Pruetz’s study, told National Geographic. “There’s this really interesting tension between cooperation and conflict. It makes me think of The Sopranos.”