Serial killer Mikhail Popkov, the former Siberian cop known as "The Werewolf", is on trial after confessing to 59 new murders and one attempted murder.
If convicted, the 53-year-old will have a total murder tally of 81 women, making him the world's third worst serial killer.
Colombian Luis "The Beast" Garavito raped, tortured and murdered 138 children, and fellow Colombian Pedro Lopez, the "Monster of the Andes", was sentenced for killing 80 girls, but is believed to have murdered 300.
American serial killer Gary Leon Ridgway, also known as the Green River Killer, was convicted of 48 murders, but is presumed to be responsible for more than 90.
Popkov, who is serving life behind bars for 22 murders, killed the women during an 18-year rampage to "cleanse" the streets of Angarsk, Siberia of prostitutes.
He is quoted as saying: "They abandoned their husbands and children at home and went out to party as if it was the last day on earth."
However, most of his victims were not prostitutes, but women with ordinary family lives; one of the women he murdered was a teacher at his daughter Katya's music school.
Popkov embarked on his killing spree, he has told authorities, because of infidelity by his wife, Elena, who has described him as "a perfect husband and father".
But he apparently targeted women who resembled his mother, who he claims abused him in childhood.
The 53-year-old made his new confessions about the additional 59 victims last year, and a Siberian court charged him with the murders.
Senior investigator Andrei Bunayev told The Mirror Popkov had given details in some of the cases.
"He names the places where bodies are hidden. We find these bodies, and check his involvement," Bunayev said.
"He says very clearly, when and what was done. We are looking for evidence that confirms his words. A large number of episodes are confirmed."
But Popkov had been "rationing" his confessions, police believe to delay his transfer from a detention facility to the prison where he would serve his life sentence.
For the past six years, police have been investigating murders in Angarsk and the Irkutsk Oblast region where dozens of women were raped and killed in secluded spots.
Popkov was arrested in 2012 and convicted and sentenced in 2015 to murdering the 22 victims, whose cases have been closed.
n one of the murders, Popkov beheaded the woman. In another, he gouged out her heart.
While off duty during his career as a police officer, Popkov would enter nightclubs or restaurants in his police uniform.
He would offer mostly drunk young women a "safe" ride home, often in his police cruiser.
He would then drive them to remote locations, rape them and kill them with an axe, knife or screwdriver.
He abandoned their naked, dismembered bodies to be found, giving rise to the then unidentified killer's nickname of "the werewolf" or the "Angarsk maniac".
On the surface, Popkov was a devoted family man and police officer.
For two decades, he eluded police investigators who ignored evidence that the mystery killer could be one of their own.
The only victim who escaped his brutal attack, known only as Svetlana M, told detectives an officer in a police car had given her a lift, then took her to a forest, forced her to strip before smashing her head against a tree trunk.
But after Popkov's wife gave him an alibi, police did not investigate further.
Former policeman Nikolai Kitaevlater said that Svetlana M had "clearly confirmed" a picture of Popkov as her attacker, but investigators chose to believe Popkov's wife.
Last month, Popkov told the Russian Meduza news site 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, realising it wasn't so scary after all," he said.
He said he gave women lifts and targeted those who were drunk or living in a way he saw as immoral, telling Meduza that "any society condemns the behaviour of a debauched woman".
He would only attack the kind of woman who "behaved as if she didn't care where we went and the most important thing to her was partying".
Sometimes he would also have sex with the bodies after the women were dead.
When he retired from the Siberian police force in 1998, the killings continued.
The unsolved murders in the Irkutsk district were re-examined in 2012, when 3,500 police officers in the Irkutsk region were forced to give DNA samples.
Investigators had matched the make of police cars to tracks had been found at the crime scenes, and Popkov's DNA matched evidence on the victims.
They have since described him as a "homicidal maniac" who had "an uncontrollable desire to commit murders".
But he has been ruled to be sane, and responsible for each murder.
Popkov's new confessions means he outstrips two men previously considered Russia's worst serial killers.
Andrei Chikatilo, aka the Butcher of Rostov, committed the rape, murder, and mutilation of at least 52 women and children between 1978 and 1990.
Alexander Pichushkin, known as the Chessboard Killer, is believed to have killed at least 48 people, and possibly 60, mostly targeting elderly homeless men by luring them with free vodka.
He is serving the first 15 years of his life sentence in solitary confinement.
Mikhail Popkov's Siberian court hearing resumes this week.