The poison attack on lions in Kenya’s Masai Mara National Reserve has claimed a third victim: Alan, a young male lion in the famous Marsh Pride.

Saturday’s attack had already claimed the lives of two lions. The lioness Bibi and another, who was mauled by hyenas beyond recognition but is likely the lioness Siena, both died on Sunday. Six members of the Marsh Pride, which was featured in the BBC documentary Big Cat Diaries from 1996 to 2008, were also sickened.

Alan was the worst-off among them but was reportedly improving. But later he separated from the rest of the pride and was too weak to avoid being trampled by a herd of buffalo. He suffered a chest wound and other injuries, according to Simon Thomsett, who examined him. A hyena came to finish him off, but he mustered the energy to crawl beneath a car. Still, his injuries were too severe, and he had to be euthanized on Wednesday.

The poisoning occurred Saturday night, when several Maasai herdsman allegedly planted the body of a dead cow laced with poison in response to an earlier lion attack on their herds.

Human-lion conflict in the Masai Mara region of southwest Kenya has been on the rise as land subdivisions and privatization reduce grazing land for cattle. At night, some Masai are known to allow their cattle into Masai Mara National Reserve, where the grazing is better—and illegal.

“It has become the norm for tens of thousands of cattle to come into the reserve at night, where in the old days this only happened under conditions of extreme drought,” said Jonathan Scott, an English zoologist who coauthored a book about the Marsh Pride.

On Tuesday, Simindei Naururi and Kulangash Toposat were arraigned in Narok, Kenya, according to the BBC. A third person is being held as a material witness for the prosecution, according to a press release from the Kenya Wildlife Service, and a fourth suspect is sought, the Associated Press reported.

Anne Kent Taylor, a conservationist at the Masai Mara reserve and a National Geographic Big Cats Initiative grantee, was distressed at the news. “I’m madder than a spitfire, and my heart is just absolutely aching,” she said.

It appears that eight lions have been poisoned, but the effects go beyond them. So far, 11 vultures have been confirmed dead, likely from feeding on the carcasses of the dead lions. There are no reports so far of sick hyenas, which have also scavenged one of the lions, but they may be affected too.

Lions in the region have been under immense pressure, Scott said. Not only are human-lion conflicts on the rise as the cattle encroach on their territory, but cattle illegally grazing on the reserve have diminished plant life, which in turn has driven away herbivores. Fewer herbivores means fewer meals and more difficult hunts for the lions.

The poisoning first came to light when a BBC film crew noticed the lions behaving strangely, spasming and struggling to stand. They called Patrick Reynolds, the manager of the nearby Governors’ Camp. Reynolds immediately contacted the mobile veterinary unit funded by the David Sheldrick Wildlife Trust. Guides from the Governors’ Camp stood watch during the night to make sure hyenas wouldn’t attack the weakened lions, and the veterinarian, Dr. Limo, arrived in the morning.

View Images After being found trampled by buffalo, Alan was darted and sedated for an examination. The vet concluded he had too many injuries and should be euthanized.

Photograph by Charlie Hamilton James

According to Reynolds, the young lion Alan was treated with the anti-inflammatory drug dexamethasone and atropine, which is an antidote for pesticide poisoning. It was likely a pesticide in the highly toxic carbamate. Carbamates such as carbofuran, which is banned in the European Union and effectively banned in the United States, have often been used to poison wildlife.

These pesticides work by blocking an enzyme called acetylcholinesterase, which breaks down a neurotransmitter called acetylcholine. Acetylcholine to builds up, causing the nervous system to overexcite, which can cause death.

Lion numbers in Africa have decreased by about 50 percent since 2003, and a recent study found their numbers are likely to fall again by half in the next 20 years without major conservation efforts. There may be as few as 20,000 left, according to National Geographic’s Big Cat Initiative.

Part of that decline has been attributed to intentional pesticide poisonings.