A recent study has theorized that a chimpanzee murder so grisly and rare that it left the anthropologist leading the study “disturbed” was most likely about sex.

The story is reminiscent of a gangster movie. The researchers involved with this study have been studying a group of chimps in western Africa referred to as Fongoli chimps since 2005. Fongoli chimps have been witnessed using rocks and sticks as tools, and are very intelligent – their daily life consists of creating and testing alliances within their community.

Their leader in 2005, named Foudouko, was known to the researchers as being the alpha male, and was nicknamed “Saddam” for his tyrannical style of leadership. The group’s beta male, Mamadou, led alongside Foudouko. However, in 2007, Mamadou suffered a leg injury, allowing other males in the community an opportunity to chase Foudouko out of Fongoli.

Foudouko disappeared. Even the researchers assumed that he had died. To their surprise, however, Foudouko returned nine months later. Mamadou’s brother, David, was now the new alpha, and Mamadou remained the beta. While certain chimps welcomed his return, Foudouko was forced to live on the outskirts of Fongoli, amongst the chimps that had suffered under his rule. He was frequently chased and attacked by the chimps he once ruled.

The study just published in the International Journal of Primatology, provides no clear answer as to what led the chimps to react so violently towards their former alpha, but suggests that the last straw for the Fongoli apes came when Foudouko attempted to court a female chimp in heat. The Fongoli community is concentrated with males, and competition in regards to sex is especially fierce amongst them.

Jill Pruetz, who led the study, attributes this skewed ratio in part to poaching, as female chimpanzees in Senegal are often taken and used to breed infants sold in the pet trade.

Chimps are prone to violence against other chimps – but killing a chimp within their own community is very rare. So rare, in fact, that this is only the ninth time researchers have been able to film it happening. The graphic video shows Foudouko being stomped on, beaten, and eventually cannibalized.

While the attack was strange and disturbing, it also provides a wealth of information for chimpanzee researchers. While Foudouko’s body was buried by the anthropologists, it will later be exhumed and studied.

It also provides interesting insight into chimps’ understanding of death. Foudouko’s body was attacked long after he had died, and researchers also noted that even after the body had been buried by them, the other chimpanzees made fearful calls all through the night, leading researchers to believe they were still afraid of Foudouko returning.

While Foudouko is gone, the drama of the Fongoli community continues. Mamadou has since been exiled from the community, presumably because of his alliance to Foudouko after his return, and David faces similar violent backlash in the form of random attacks from other members of the Fongoli chimps.