A BBC investigation has uncovered an international network of people paying Indonesians to torture and kill baby monkeys on film.
Warning: This story contains disturbing content describing violence towards animals.
One man, called "the Torture King", told the UK broadcaster a poll was set up to take customers' requests for the torture.
"Do you want a hammer involved? Do you want pliers involved? Do you want a screwdriver?" he told the BBC.
He called the resulting videos "the most grotesque thing [he has] have ever seen".
Hundreds of people around the world were allegedly paying customers.
The long-tailed macaque abuse ring began on YouTube before moving to private groups on Telegram, the investigation found.
At least 20 people are now under investigation globally, with several arrests made already.
"BBC journalists went undercover in one of the main Telegram torture groups, where hundreds of people gathered to come up with extreme torture ideas and commission people in Indonesia and other Asian countries to carry them out," the broadcaster's report said.
A BBC reporter also visited a suspected monkey torturer while undercover. They secretly filmed the encounter.
"The sadists' goal was to create bespoke films in which baby long-tailed macaque monkeys were abused, tortured and sometimes then killed on film," the report added.
"The Torture King", American Mike McCartney, was reportedly a key distributor of the videos in the US.
"It's no different than drug money," he said.
"Drug money comes from dirty hands, this money comes from bloody hands."
An international law enforcement effort is underway.
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