As the flames were dying down in the wake of a deadly riot at a high-security penal colony in Siberia in April 2020, a more brutal wave of violence was brewing.

The clashes at Penal Colony No. 15 in Angarsk, an industrial city of more than 200,000 people near Mongolia, were sparked after a guard beat an inmate, prisoners and monitors said.

Prison officials put forward a disturbing detail from the riot, which left one prisoner dead: several inmates had cut open their wrists with glass shards from broken surveillance cameras.

But the riot was just the beginning.

In the months that followed, prison guards embarked on a brutal campaign of retribution for the mutiny, turning inmates on each other to extract confessions with beatings and sexual violence, according to interviews and testimonies reviewed by AFP.

Former inmate Alexei, whose name has been changed to protect his safety, described being beaten while bound and hung by his legs before confessing to breaking two cameras in the unrest.

Then the punishment got worse.

"Just for that, they broke my fate," the 25-year-old told AFP, referring to an expression in Russia's prison lexicon meaning to have been raped by fellow inmates.

Alexei and another now released inmate, 40-year-old Rustam -- who spoke to AFP from his native country Tajikistan and whose name has also been changed -- said they were transferred from Angarsk to Irkutsk's Detention Centre No. 1 after the unrest.

It was there, they said, that they were assaulted by inmates on the orders of prison guards.

One of those inmates, Denis Golikov, said he was instructed to go as far as possible to get necessary confessions from 150 prisoners between April and July 2020.

"Everything -- except corpses -- is permitted," he said in hand-written testimony obtained by AFP.

Torture and sexual violence inflicted on inmates is systemic in Russia's vast penitentiary system, prison monitors say.

Just this week, authorities launched a probe into a case in the central city of Saratov, after a video released by the anti-torture project Gulagu.net showed a naked man being violated with what appears to be a stick at a prison hospital.

The video, which resulted in the firing of five prison officials Wednesday, was part of a trove of over 1,000 files allegedly showing instances of torture in prisons across the country.

Gulagu.net also brought to light the Angarsk case.

In December 2020, the project reported the case of Kezhik Ondar, who like Alexei and Rustam was transferred to Detention Centre no. 1, where he suffered serious injuries after he was sodomised with an immersion water heater.

Within weeks, a special commission was dispatched to Irkutsk.

Soon after, the head of Penal Colony No. 15 during last year's unrest, Andrei Vereshchak, was placed under house arrest on suspicion of corruption.

Torture and sexual violence inflicted on inmates is systemic in Russia's vast penitentiary system, prison monitors say
Torture and sexual violence inflicted on inmates is systemic in Russia's vast penitentiary system, prison monitors say AFP / Dimitar DILKOFF

Four prisoners and three officials were eventually indicted for raping Ondar, while another official was implicated for a similar case at another facility in the region.

And late last month, the Investigative Committee, which probes major crimes in Russia, said it was investigating "systemic torture" between April and December 2020 at Penal Colony No. 15, Detention Centre No. 1 and another facility in the Irkutsk region.

Sixteen prisoners have been accused of rape.

Ondar's lawyer Dmitry Dmitriyev calls his client's case a "catalyst".

"If it hadn't been for the media fuss, they would have covered it up," he said.

The Federal Prison Service (FSIN) did not respond to AFP's requests for comment.

Gulagu.net collected testimonies from three prisoners who participated in the systematic torture of inmates at Detention Centre No. 1.

Vladimir Osechkin, who runs Gulagu.net from France, said the torturers speak out because they do not want to be solely culpable for the crimes.

The authorities "launch criminal cases against the sadists who carried out the torture, but not against those who ordered it", he said, stressing that Russian penal facilities "systematically" use detainees to punish other inmates.

While Osechkin described the recent criminal investigations as "historic", he said they concern only a "small" number of the rape victims of the Angarsk riot.

He estimates the true number at 200.

The Kremlin has appeared to take prison torture cases seriously, saying this week that if the Saratov rape video is authentic, it calls for a "serious probe".

But Osechkin and Dmitriyev believe true justice is never served in such cases.

The investigators "will not go so far as to say it was a planned punitive operation or prosecute the organisers," Dmitriyev said of the retributive Angarsk campaign.

For the victims, life will never be the same.

Back in Tajikistan, Rustam is still healing from beatings that caused him to lose consciousness.

Alexei said he is still recovering after his prison rape.

"My family abandoned me, everyone turned away from me," he told AFP.

Ashamed to return to his hometown, he is now living in another town in the Irkutsk region.

"I've lost everything," he said.