Mikhail Popkov is said to have admitted killing 81 women
Mikhail Popkov has already been convicted of raping and killing 22 women, and has now confessed to 59 more between 1992 and 2010, according to Interfax news agency.
He appeared in court in the Siberian city of Irkutsk for a first hearing during which prosecutors read out the charges.
Popkov killed the women with a hammer or axe after offering them lifts late at night, sometimes in his police car, while he was off duty near his hometown.
Russian media have nicknamed him "the werewolf" and the "Angarsk maniac".
Popkov, 53, told the Meduza news site in December that he viewed himself as a "cleaner" who was purging his city of prostitutes.
He said he had targeted women who were drunk or he viewed as immoral.
His victims did include prostitutes and drug addicts, but most were ordinary women with families, said investigator Yevgeny Karchevsky.
He was finally caught in 2012 after investigators DNA-tested people who drove cars matching tyre tracks found at the crime scenes.
Popkov later showed police where he had buried his victims' bodies.
"His diagnosis is homicidal maniac, that he has an uncontrollable desire to commit murders," Mr Karchevsky told Meduza.
He added that Popkov is seen as having a personality disorder but is not judged to be insane.
If convicted over the 81 deaths, he would be the most prolific killer in Russia's recent history, eclipsing "chessboard killer Alexander Pichushkin, who murdered 48, and Andrei Chikatilo, who killed 52.
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