A court in Siberia has opened hearings in the trial of a former policeman who is charged with the murder of 60 people.

Mikhail Popkov, from the eastern Siberian city of Angarsk, was first arrested in 2012 and sentenced to life in prison for the murder of 22 women. While in custody, Popkov confessed to killing 20 more between 1992 and 2010.

Local police have for years been investigating murders in the Irkutsk region where dozens of women were raped and killed in secluded spots.

The latest charges against Popkov include 60 counts of murder, which could make him Russia's biggest serial killer in at least the last 100 years. Prosecutors began reading out the charges on Wednesday and adjourned the hearing until Monday.

Psychiatric tests run on Popkov have shown that he is sane.

He is already serving a life sentence after being convicted in 2015 of raping and killing 22 women, and the attempted murder of two more.

Popkov killed his victims after offering them rides late at night, sometimes in a police car, while he was off-duty around his home city of Angarsk near Irkutsk.

He has been nicknamed "the werewolf" and the "Angarsk maniac" by Russian media.

If convicted of 81 murders, he would exceed the total number of people killed by notorious figures like "chessboard killer" Alexander Pichushkin who killed 48, and Andrei Chikatilo, who was convicted of 52 Soviet-era murders.

At Wednesday hearing, which was closed to the media to avoid making public details of the sexual nature of his alleged attacks, prosecutors read out the charges against him, Interfax news agency reported.

Popkov has reportedly described himself as a "cleaner" who was purging the city of prostitutes.

The victims were all women aged between 16 and 40 except for one where Popkov killed a male policeman.

Last month, Popkov told the Meduza news site he had killed his victims with a hammer or an axe and that after his first murder, he felt little fear of discovery.

"The same situation would come up again, only this time I did everything more cold-bloodedly, controlling myself, realizing it wasn't so scary after all."

He said he gave women lifts and targeted those who were drunk or living in a way he saw as immoral, telling the news site that "any society condemns the behavior of a debauched woman."

He said he would only attack a woman who "behaved as if she didn't care where we went and the most important thing to her was partying" and linked the killing spree to suspicions that his wife was unfaithful.

The murders took place while he was a serving police officer and after his retirement in 1998.

It was only in 2012 that he was caught when investigators re-examined the cases and carried out DNA testing, focusing on those who drove a make of car whose tracks had been found at crime scenes.

Popkov later showed investigators the crime scenes and where the bodies were buried.

Speaking to Meduza, lead investigator Yevgeny Karchevsky described him as a "homicidal maniac" who had "an uncontrollable desire to commit murders."

Although Popkov is believed to have a personality disorder, he is judged to be sane and responsible for his crimes, Karchevsky said.

Although there were a number of prostitutes and drug addicts among the victims, most were ordinary women with families, he said.

"He wasn't cleaning up the town from sin -- that was made up by the media," he added.