A Russian court has sentenced a distinguished historian known for re-enacting Napoleonic battle scenes to 12-and-a-half years in jail after convicting him of the murder of his young student lover, whom he dismembered.

Oleg Sokolov, 64, a former history professor at St Petersburg State University, was found in a river in November last year with a bag containing the severed arms of Anastasia Yeshchenko, a 24-year-old postgraduate.

Sokolov pleaded guilty to her murder, but told the court it had not been premeditated and that she had driven him to "a state of complete insanity" by making insulting comments about his children from another relationship.

The prosecution had asked the court in St Petersburg to jail him for 15 years. Sokolov said he was tormented by the crime and sought a more lenient sentence.

As she handed down the verdict, the judge said Sokolov had shot Ms Yeshchenko four times with a rifle before dismembering her with a knife and saw, taking the body parts out in bags and dumping them in St Petersburg's River Moyka.

He got rid of her phone in the river near his home, but was caught while disposing of the body parts.

When the severed arms failed to sink, he got into the frigid waters and was then physically unable to get back out because of the cold, the judge said. He was subsequently caught.

The court also found him guilty of weapons possession and that was factored into his sentence.

Sokolov is an expert on Napoleon Bonaparte and was awarded the Legion of Honour order of merit by France