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 licence 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.