Moscow, Russia - Russia said Wednesday that it had not changed its policy of pardoning prisoners in exchange for fighting in Ukraine after local media reported a "satanist" killer had been released.

Nikolai Ogolobyak (33) was sentenced to 20 years for the ritualistic murder of four teenagers in 2008. He was freed earlier this month after fighting in Ukraine, local media reported this week.

"Now everyone is studying the pardon lists very closely," Kremlin spokesman Dmitry Peskov told reporters.

"But I repeat once again, we are talking about certain conditions that are related to being on the front line," he said, adding, "There have been no revisions in this regard."

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Ogolobyak and six other members of a self-proclaimed cult were handed lengthy jail terms for the gruesome murders, which took place in Russia's Yaroslavl region 15 years ago.

He would have been jailed until 2030 but was drafted into one of Russia's Storm-Z battalions for offenders and convicts after the conflict began, the 76.RU media outlet reported.

"After being wounded, he is disabled," Ogolobyak's father told the outlet.

Russia has probably recruited 100,000 people from prisons to fight in the conflict, the head of an independent prisoners' rights group, Olga Romanova, has estimated. According to Ukrainian President Volodymyr Zelensky, Moscow is now using convicts to replace the bulk of its soldiers lost in combat.

"At this stage, the Russian army has made prisoners the main source of replenishment of losses on the battlefield," he said in a briefing Wednesday, citing intelligence.

The practice is controversial, and local media have reported several instances of released prisoners going on to commit serious offences, including murders, after leaving the army.

The Kremlin acknowledged the use of prisoner recruits to fight in the conflict earlier this month but said convicts could "atone for their crime on the battlefield with blood."