The group of prison service employees, “acting deliberately, clearly exceeding their official powers, used violence against a prisoner,” investigators said.

Human rights activists regularly report torture, humiliation, and beatings in Russian prisons, but the leak of such an explicit video is rare.

The branch of the Investigative Committee for the Volga city of Yaroslavl, where the video was shot at a penal colony, said “today six people have already been detained.”

“The criminals delivered multiple blows with hands, feet, and unidentified objects to the man’s torso and limbs,” it said in a statement.

The 10-minute video posted by the Novaya Gazeta newspaper on Friday shows a group of 18 uniformed men methodically beating a man who is pinned down on a table as he groans and pleads for mercy. They also pour water on his head.

The video clearly shows the men’s faces. Novaya Gazeta reported that it was shot in June 2017 but criminal action was only launched after the publication of the video.

Rights group Public Verdict, which passed the video to Novaya Gazeta, said Monday its lawyer Irina Biryukova, who represents the tortured prisoner, has fled Russia fearing reprisals and had asked for state protection for family members.

Investigators said they had identified all those involved and were going through legal procedures to detain the rest of the participants.

They said that they would also look at the actions of the prison governor and leading regional prison officials.

The video was shot with a portable video recorder that, according to the law, prison officers are obliged to carry.

Last year, Novaya Gazeta reported an inmate who was sentenced for taking part in protests against the return of Vladimir Putin to the Kremlin in 2012 was tortured there in a punishment cell.