Mikhail Popkov, a former police lieutenant from the Irkutsk region of Siberia, was previously convicted of murdering 22 women between the ages of 18 and 50.
He was sentenced to life in prison at the end of a 2015 trial, after which detectives began working on further leads.
The 54-year-old has now been convicted of killing at least 78 victims in total, while working as a police officer.
The verdict of the second trial, held at Irkutsk’s regional court, also stripped Popkov of his Police Junior Lieutenant rank and his state pension, according to The Siberian Times.
Popkov previously claimed that his aim was to “clean streets of Siberian cities of immoral women".
“He said he ‘sentenced them to death’ as soon as they agreed to share a drink with him,” said state prosecutor Alexander Shkinyov.
“He forgave three women because they didn’t agree to drink with them. He escorted these women home and even helped some of them to carry their bags. He clearly loved killing.
"Some victims had 145, or even 170 knife wounds.”
In testimony leaked earlier this year to Komsomolskaya Pravda, the 54-year-old revealed how he exploited the cover provided by his job.
Popkov told detectives how he offered his victims lifts in his police car before taking them to remote locations and raping and murdering them.
“The victims were those who, unaccompanied by men, at night, without a certain purpose, were on the streets, behaving carelessly,” he said.
“[They] were not afraid to enter into conversation with me, get into my car, and then go for a drive in search of adventures, for the sake of entertainment, ready to drink alcohol and have sexual intercourse with me.
“Not all women became victims but those of a certain negative behaviour. I had a desire to teach and punish.”
Detectives arrested Popkov in 2012 and extracted a number of confessions from him about the murders, which were committed from 1992 to 2010.
The second guilty verdict means that he is now Russia’s most prolific serial killer from the 20th and 21st Centuries.
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