MOSCOW - A Russian who participated in the torture of a captive in Syria and filmed the prisoner’s dismemberment and beheading has been identified by media outlets as a former policeman from Stavropol in southern Russia, who served as a mercenary employed by the Wagner Group, a Kremlin-sponsored private military contractor.

A video of the four Russian-speaking men taking part in the gruesome murder was first posted online in 2017 and new footage of the killing emerged on social media this month. The first video showed the assailants smashing the victim with a sledgehammer and dismembering him. A second video was posted on a closed account for Wagner members on the Russian social media site VKontakte, but was quickly unearthed by investigative journalists.

Novaya Gazeta, an independent newspaper, said it has used facial-recognition technology to identify one of the mercenaries and then corroborated its findings with his Russian passport and leaked internal Wagner documents, indicating the former policeman joined the Kremlin-tied private army in 2016. The newspaper named the man as "Stanislav D" but has withheld his family name, fearing reprisals against his relatives.

A screengrab from video published by Novaya Gazeta purports to show Stanislav D as the man on the left.

Novaya Gazeta’s discovery has been confirmed by the online investigative news site Bellingcat, which last year accurately identified the would-be GRU military intelligence assassins of former spy Sergei Skripal, who survived a bid to kill him in England using the nerve agent Novichok.

The Kremlin said Thursday it had no knowledge of the slaying or the involvement of Russian mercenaries.

“This has absolutely no relation to Russian soldiers, no matter what is being published about it,” said Dmitry Peskov, a spokesman for Russian President Vladimir Putin. Peskov said he had not watched the footage. Foreign ministry spokesperson Maria Zakharova said last month there was nothing the Russian government could do to prevent “private Russian citizens from acting as bodyguards overseas.”

"Stanislav D" reputedly joined Wagner as a reconnaissance gunner to “defend the interests of the Russian Federation,” according to leaked Wagner documents. He has declined to comment to local reporters on the grisly killing or the allegations against him. In the posted video footage, four men in military-style clothing are seen beating the prisoner with a sledgehammer, beheading him and amputating his arms by hacking at them with with a trenching shovel before igniting his body using gasoline.

The victim is believed to have been 31-year-old Mohammad Taha al-Ismail Abdallah from eastern Syria, who was conscripted into the Syrian army and then deserted. In the footage, one of his killers is heard shouting, “Cut him harder. Come on! Break his spine! Keep the legs. We’ll hang him by the legs.” The killers are initially wearing masks but remove them for a group photograph. Another severed head is also seen in the video.

For the group photograph, the men posed with their victim’s suspended body. Across its torso, they wrote: “For the VDV [Russian airborne forces].”

FILE - Kremlin-linked businessman Yevgeny Prigozhin gestures on the sidelines of a meeting at the Konstantin palace outside St. Petersburg, Russia, Aug. 9, 2016.

The Wagner Group is a military contractor believed to be run by Yevgeny Prigozhin, a businessman nicknamed Putin’s Chef because he holds lucrative Kremlin catering contracts. Prigozhin and Putin first became friendly when Putin was an official in the city government of St. Petersburg. The Kremlin has repeatedly denied it has any knowledge of Wagner Group operations.

Prigozhin was indicted last year by U.S. special counsel Robert Mueller for overseeing a troll factory that led Russian meddling in U.S. elections. Since the indictment, Prigozhin has emerged as a key figure in what analysts say is a wide-ranging Kremlin influence operation aimed at boosting Russian clout in Africa and the Middle East at the expense of Western powers.

Wagner mercenaries, many former Russian soldiers who are servicemen on a leave of absence, have been spotted fighting in Ukraine’s eastern Donbas region, appeared in Crimea before its annexation by Moscow and have fought in Libya. Wagner mercenaries have also been present in the Central African Republic, Sudan and Mozambique.

In September as many as 35 Wagner mercenaries were reported to have been killed in Libya while fighting for Khalifa Haftar, a military general during the rule of the late leader Muammar Gaddafi. Haftar launched an offensive earlier this year on the Libyan capital of Tripoli. Seven Wagner Group fighters were killed in October separate in clashes involving Islamic State-linked insurgents in Mozambique, according to the English-language newspaper Moscow Times.

Thousands of Russian contractors fought in Syria in Moscow’s intervention first launched in 2015 to prop up the government of Bashar al-Assad.