The details are sketchy. The incident occurred on May 22 on Tibet’s North Col route up Everest, according to a British climber who witnessed it. The climber in question, a Han Chinese whose name we still don’t know, drew suspicion when he camped apart from the other two Chinese expeditions on the mountain. If you’re trying to poach Everest—that is, climb it without a permit—keeping to yourself and camping away from other groups is a dead giveaway.

As with climbing from the more popular south (Nepalese) side of the mountain, permits on the Chinese side of Everest represent only a small portion of the total cost—$25,000 on the low end. Even so, the risk of getting caught, having to pay a large fine, and forfeiting the expense and effort that goes into the rest of the trip usually dissuades people from attempting to climb it illegally. Plus, the vast majority of climbers enlist the services of professional guides, who wouldn’t even consider signing up an unpermitted climber. Still, it does happen.

But how exactly a group of graduates of the Tibet Mountaineering Guide School (TMGS), who were working as rope fixers on behalf of all the other commercial expeditions, figured out that he was climbing without a permit, and why they decided to do what they did, remains unclear. (Attempts to reach officials at TMGS have thus far gone unanswered). The incident started at 25,500 feet. The TMGS grads confronted the Chinese climber, who wielded his ice axe as a weapon. They subdued him, bound his hands, and marched him down to the North Col at 23,000 feet.

The British climber, who asked not to be named, described the incident in an email to Billi Bierling, the assistant of Everest historian Elizabeth Hawley. It read in part:

“I did see the permitless chap being ushered down the hill. The Tibetan rope fixers were sent up to get him. I saw them bringing him down the ropes from the North Col to [advanced base camp]. It was disgraceful. They literally kicked him down the ropes. It was a disgusting example of a pack of bullies egging each other on and literally beating him down the hill. It was absolutely unnecessary as he was offering no resistance and was scared out of his mind. The Tibetans should, and could, have just escorted him down the hill and let the authorities deal with him.”

Kari Kobler, 57, a Swiss guide and the proprietor of one of the world’s largest outfitting operations, Kobler & Partner, also encountered the procession. Kobler has climbed Everest five times and has been guiding the mountain since 2000. He filmed the brutal scene playing out in front of him but hasn’t made the footage public. Though he wouldn’t let me watch the video when I met with him over lunch in Kathmandu, he did briefly describe it after I mentioned that I’d heard rumors about it.

The men dropped their captive, “like a rucksack with an oxygen tank, but actually it is a human being,” says Kobler, who believes that the incident could inflame tensions in the region or give the Chinese authorities an excuse to further restrict Tibetan freedom. “It’s a tough one. It’s really tough. I know all of them.”

“The reason I made this video—If I don’t have proof, nobody will believe me. [The TMGS grads] can lie and say nothing happened. But now I can go to them and say, ‘Please, young boys.’

Kobler says he has no plans to release the video, though he did show it to Hans Schallenerger, the Swiss-born head of Chinese mountain gear maker Ozark—his main gear sponsor and a major supporter of the Tibet Mountaineering Guide School. Together they decided to handle the incident internally, so as not to risk an overreaction by the authorities. In a recent email, Kobler wrote: “We decided instead of making bad news to the students to teach them what they have to do in such situation.”

However, this isn’t the first time they’ve had problems with graduates of the non-profit school, which was founded in Lhasa in 1999 and provides free job training for locals who want to work in the mountaineering industry. “They did some other big mistakes [in addition to this incident],” says Kobler. “I don’t want to say now when the [audio] recorder is working but they made a big mistake that has nothing to do with the Chinese; it has to do with oxygen.”

The insinuation, of course, is that TMGS grads may have been involved in the theft of high-priced oxygen canisters—a serious crime that can endanger the lives of the climbers who pay roughly $1,000 per bottle. Over the years, there have been reports of both theft and the sale of fake oxygen bottles, though prosecution for such crimes is rare. Theft is, in fact, so common that some outfitters like Kiwi Russell Brice, who until 2007 operated his company, Himalayan Experience, on Everest’s north side, haul cable locks up the mountain to secure their precious bottles.

“If someone needs a cylinder in an emergency” he recently wrote in an email, “they just need to call on a radio and we can tell them the combination of the padlock.”

The question now is whether the school’s supporters, like Schallenerger, and the outfitters that hire their graduates are capable of preventing future incidents from occurring.

As for the permitless Chinese man, Kobler isn’t sure what happened to him, though he did survive and walk off the mountain. “He’s not killed,” says Kobler. “They beat him only.”