MOSCOW (AP) — A court in Russia's eastern Siberia has convicted a former policeman of murdering 56 women, bringing the number he is believed to have killed to at least 78.

The court on Monday found Mikhail Popkov, from the eastern Siberian city of Angarsk, guilty of the murders between 1994 and 2000 and sentenced him to life in prison. Popkov, who was arrested in 2012, is already serving life for 22 other killings.

The verdict makes him Russia's most prolific serial killer in at least the past century.

Local police have for years been investigating murders in the Irkutsk region, where dozens of women were raped and killed in secluded spots.

Psychiatric tests run on Popkov have concluded that he is sane.