Vyacheslav Grigoryev, 32, was suspected of murdering Yury Kamagin, 31, who went missing in February after they drank alcohol together. Kamagin's body was later discovered in a river.
However, Grigoryev refused to plead guilty at first and there was not enough evidence to convict him, the spokesman said.
The criminal probe was led by 27-year-old investigator Regina Pak, who decided to prove that Grigoryev was guilty by collecting new evidence. Two months later, however, the man came to the investigative department where he "fell on his knees and said he was in love with her," the spokesman said.
He then "confessed to the crime, describing all the details of the murder and showed where he had hidden the corpse," the spokesman added. Grigoryev said he strangled his friend during a quarrel and hid his body in the river.
Grigoryev said in court he admitted his crime in order not to "ruin the beloved investigator's career with an unsolved case." He now faces up to 15 years in prison.
