In the video, a man in an orange jump suit kneels beside a lake in Syria and confesses in Russian to spying on Islamic State militants. Another Russian speaker, this one in camouflage fatigues, then uses a hunting knife to hack off the kneeling man's head.
When Islamic State posted this footage online on Dec. 2, it brought the distant Syria conflict home to ordinary Russians. Here, in high-definition video, appeared to be one young Russian killing another for reasons few people could understand.
It also opened up another mystery.
The prisoner and alleged spy in the video said his name was Magomed Khasiev, that he was from Russia's mainly Muslim region of Chechnya, and that he worked for Russian intelligence.
Pro-Kremlin Chechen leader Ramzan Kadyrov quickly denied Khasiev was a spy.
But interviews with more than a dozen people who knew Khasiev in Russia suggest the 23-year-old man had connections to both Muslim groups and Russian security and seemed to live a double life.
An ethnic Russian born to a non-Muslim family in Russia's industrial heartland, Khasiev spent his teenage years among Chechens who knew him as a devout Muslim and a fluent Chechen speaker. Some of his Chechen friends went off to fight for Islamist militants in the Middle East, and encouraged him to join them.
In his other life he associated with non-Muslims, had a friend in the police, and had a license from the Interior Ministry to work as a security guard, according to a former teacher, a friend, and staff of several security companies. For some purposes, including his work, Khasiev used the name he was given at birth: Yevgeny Yudin.
If his testimony on the video is to be believed, Khasiev ended up caught in the murky world between official Russian involvement in the conflict in Syria and the jihad that several thousand citizens of Russia and other former Soviet republics have joined.
Neither Russia's Federal Security Service - the intelligence agency Khasiev claimed he was working for - or Russia's Interior Ministry responded to requests for comment on the case.
According to his file at an orphanage in Chechnya, Khasiev was raised for the first decade of his life by his mother, an ethnic Russian. When he was 10, she handed him to the orphanage for reasons the file does not make clear. Soon after, the documents show, his mother died of tuberculosis.
In the orphanage, Khasiev, or Yudin at that time, learnt Chechen, gave himself the Muslim first name Magomed and converted to Islam.
The former head of the orphanage, Ruslan Yusupov, remembers Khasiev playing with his own children and grandchildren. "He was soft as a kitten. He loved attention and care so much."
After three years, Khasiev was adopted by a Chechen family and took the last name of his adoptive mother Markha Khasieva. But she returned him to the orphanage a year later because of tensions between her and other relatives. Khasieva told Reuters she had nevertheless stayed in touch with the boy and cared for him.
In 2008, Russia's then Interior Minister, Rashid Nurgaliev, visited the orphanage to talk to potential new recruits for the Suvorov academy, an new elite military school.
According to orphanage staff, Khasiev, then 16, was keen to enrol
l but was rejected as too old. His best friend at the orphanage, Minkail Temiev, did qualify.
Khasiev was sent to a college in Maykop, capital of the predominantly Muslim Russian region of Adygeya, some 500 km (310 miles) from the Chechen capital Grozny.
There, according to friends and family, Khasiev moved in two sets of social circles.
In one, he maintained his Chechen identity and stayed in touch with his adoptive family and old friends, including Temiev. According to orphanage staff, Temiev in fact followed Khasiev to Maykop.
At college, Khasiev was registered by his Russian name. But he told teachers he wanted to be called Magomed. "At first, he corrected his teachers," his supervisor Tatiana Maystrevskaya recalled. "I told him: Once you change your documents, I will call you Magomed. He didn't object to that."
Acquaintances outside college, many of them Chechens, always knew him as Magomed. "He wasn't any different from us, he spoke pure Chechen. Many people didn't even know he was Russian," said one of Khasiev's Chechen friends.
Khasiev eventually changed his name officially to Magomed Khasiev by applying for a new passport, according to Viktor Zyzin, a close friend and an ethnic Russian.
But despite his insistence on using a Muslim name, Khasiev did not appear to be a Chechen nationalist or radical, Zyzin said. A 2011 posting on Khasiev's account on Vkontakte, the Russian version of Facebook, shows him posing next to a poster of Chechen strongman Ramzan Kadyrov. The Chechen leader helped the Kremlin defeat a Muslim insurgency in the North Caucasus and is considered by Muslim militants to be an infidel.
And Khasiev had plenty of non-Muslim friends, including Zyzin and an ethnic Armenian called Grant.
In the video of his beheading, Khasiev describes Grant as an old acquaintance and the conduit to Russian special services through which he passed the intelligence he collected on Islamic State militants.
A Chechen friend of Khasiev told Reuters Grant served in the police. Two other people who knew Khasiev, including Zyzin, said they had met Grant but did not know where he worked.
Reuters has not been able to establish Grant's family name or other details about him. Officers in the regional police department of Adygea and the city police of Maykop said nobody of that name worked for them. The Interior Ministry in Moscow did not reply to a request for comment.
At the end of 2013, Khasiev was hired by Sherif M, a security company in Maykop. According to Anzor Takhumov, head of a local security guard school, Khasiev had applied for an Interior Ministry licence to work as a guard a few years earlier using the name Yudin. That was also the name he used to get his job.
Just a few months after he began working, Zyzin said, Khasiev sold an apartment he had bought under a Russian government scheme designed to help orphans.
(L-R) Minkail Temiev, Viktor Zyzin and Magomed Khasiev, pose for a picture in a park in the southern city of Maykop, Russia in this handout photo provided to Reuters by Viktor Zyzin. Photo: Reuters/Viktor Zyzin/Handout via Reuters
It is not clear how he ended up in Islamic State territory in Syria, but members of Khasiev's adoptive family in Chechnya suspect his old friend Temiev may have played a role.
They believe Temiev had become radicalised. Markha Khasieva said her adoptive son had told her that Temiev had tried to recruit him to join Islamist fighters, but that Khasiev had rejected the offer. She remembers Temiev showing up at a funeral wearing a long beard, a style often associated with followers of hardline Islam. Family members joked that he looked like Karl Marx.
According to people who knew him, Khasiev enjoyed drinking and dating girls and showed no sign of Islamist sympathies. "He did not have any extremist views," said Ruslan, Markha Khasieva's nephew.
Nevertheless, Khasiev left Russia at some point last year. His adoptive family in Chechnya had little idea where he had gone. "We thought he was off working somewhere," said Malika Khasieva, his adoptive aunt.
Khasiev did keep in touch with his Russian friend Viktor Zyzin, sending him messages from the outskirts of Kobani, a Syrian town near the border with Turkey that was the centre of a battle between Islamic State and Kurdish forces.
Zyzin said he believed his friend went there to follow Temiev. But he quickly discovered that Temiev had been killed, Zyzin said, citing messages Khasiev had sent him.
In his messages, Khasiev referred to his fellow fighters as "brothers" and started using common Islamic expressions more and more often. Zyzin said his friend told him "he simply collected dead bodies ... He told me he was tired of picking up pieces."
The last message from Khasiev was in February. Zyzin had asked his friend to come home.
"He said that he may come to visit. But at the end he wrote that he got tired. He sent voice messages. Back then I realized already, that he would not come back. There is simply no way back from there."