Mikhail Popkov, 53, appeared in court in the Siberian city of Irkutsk after confessing to 59 additional murders and one attempted killing between 1992 and 2010, Interfax news agency reported.
He is already serving a life sentence for raping and killing 22 women, and the attempted murder of two more.
Popkov killed his victims after offering the women rides late at night, sometimes in a police car, while he was off-duty around his hometown of Angarsk close to Irkutsk.
He has been nicknamed "the werewolf" and the "Angarsk maniac" by Russian media.
If convicted of 81 murders, he would exceed the total of notorious figures such as the "chessboard killer" Alexander Pichushkin, who killed 48, and Andrei Chikatilo, convicted of 52 Soviet-era murders.
Wednesday's first full hearing saw prosecutors read out the accusations against Popkov.
The hearing was closed to media to avoid making public details of his alleged sexual attacks on victims, Interfax news agency reported.
Popkov has called himself a "cleaner" who was purging his city of prostitutes, according to reports.
He said he gave women lifts and targeted those who were drunk or living in a way he saw as immoral.
The crimes were committed during Popkov's career as a policeman and after he retired in 1998.
Popkov was only caught in 2012 after investigators re-examined the cases and carried out DNA testing of residents, focusing on those who drove a make of car whose tracks had been found at crime scenes.
Popkov later went with investigators to the crime scenes and showed them where the bodies were buried.
Investigator Yevgeny Karchevsky, who worked on the case, told Meduza: "His diagnosis is homicidal maniac, that is he has an uncontrollable desire to commit murders."
Popkov is seen as having a personality disorder but is judged to be sane and responsible for his crimes, the investigator said.
Victims included prostitutes and drug addicts but most were ordinary women with families, Karchevsky said.
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