Maxim Usik had an argument with his grandmother in December 2012 about how much alcohol he had consumed, RIA Novosti said.
He then used a knife to attack the grandmother, who had raised him since his mother's death. Usik then wrote "sorry" on her body, RIA Novosti said, and hid the body in a wardrobe.
Usik pleaded guilty to the crime, which occurred in Vyborg, prosecutors said.
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