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A savage killer who decapitated one woman and carved the heart out of another in a chilling campaign of violence may have murdered "many" more victims, police fear.

Mikhail Popkov , known as "The Werewolf" was jailed for life earlier this year after he was found guilty of killing 22 women.

The 51-year-old former policeman, who also raped most of his victims, is expected to face new charges next year after officials confirmed he was still being investigated over "dozens" of unsolved murders in Siberia and the Russian Far East going back to the 1990s.

One anonymous source close to the investigation claimed the married father-of-one could have committed another 20 murders.

Another indicated his full toll could be as high as 61, but officials refused to comment on the figures.

(Image: Channel 1;The Siberian Times)

He avoided arrest for many years because police could not contemplate that a serving officer - one of their own - could also be a mass killer.

Popkov gave lifts in his police car to women who he then murdered with axes, knives or screwdrivers.

His victims' bodies were invariably found dumped naked in woods, on the roadside and in a cemetery.

One woman had been decapitated while another's heart had been removed.

After he was detained in 2012, he told police he wanted to "cleanse" prostitutes from the streets of his home city of Angarsk in Siberia.

The overwhelming majority of his victims were women enjoying a few drinks on a night out.

"One theory is that he targeted women in revenge for his fear that his wife had cheated on him," reported The Siberian Times .

A massive deployment of detectives is now working with Popkov, convicted to a life sentence in January this year.

One source claimed he has confessed to another 11 killings, while another 39 unsolved cases are being re-examined for signs of his "trademark style" of butchery.

(Image: Alamy)

Law enforcement officials are now discounting his earlier claim to have halted his killing spree in the year 2000 when he "lost his sexual potency", it is understood.

Senior investigator Ivan Rastorguev, said: "A criminal case with new episodes will be passed to the court in 2016."

He revealed: "We are checking all the unsolved murders of women since the 1990s."

The man known as "The Werewolf" is believed to have confessed to new murders.

"We are working with Popkov himself," said Rastorguev, head of the Russian Investigative Committee's criminology department in Irkutsk region.

After quitting the police, Popkov bought and sold cars, travelling through eastern Russia.

Now all regions he visited have been warned that he may have committed murders of young women.

Popkov's wife Elena, 49, and daughter Ekaterina, 27, a teacher, initially stood by him, refusing to believe he was a mass killer.

But earlier this year they stopped visiting him in detention.

They moved to another Russian city to start new lives.