Oleg Sokolov, 63, a professor of history at St Petersburg National University, confessed to the murder of the young mistress and identified her after arguing.

Sokolov told investigators that he shot and killed Anastasia Yeshchenko, 24, his lover and former student, after an argument, sawing the victim's head, hands and feet, and then planning to throw it away. her body.

"He has admitted his sins," said Alexander Pochuev, Sokolov's lawyer, adding that on 10 November, the client was deeply sorry about what he had done and was cooperating with the police.

Sokolov was arrested by police on 9 November after being pulled up from the cold Moika River with a backpack containing women's arms. He is said to be drunk and falls into the river while trying to kill the victim.

Officials have discovered Yeshchenko's intact body in Sokolov's home. She is a co-author with a professor in many works. They both studied French history and liked to transform into historical figures.

Lawyer Pochuev said that maybe Sokolov may have stress or emotional disorder. "He is an old man," Pochuev said and said his client was being treated for hypothermia at a local hospital, but declined to provide further details.

Sokolov is a famous Russian historian of Napoleon Bonaparte with many books written about this king. Professor has served as a historical advisor for many films.

In 2003, he was awarded the Order of the North Big Boi Tinh by French President Jacques Chirac. Sokolov is also a member of the French Academy of Social Sciences, Economics and Politics (ISSEP). However, in a statement released yesterday, the institute said he was stripped of membership.

According to colleagues and students, Sokolov is a talented but mentally unstable and alcoholic. Everyone in the school knows his relationship with Yeshchenko but avoids discussion because "it's her own business".

Local media reported that Sokolov assaulted and threatened to kill another woman in 2008 but was not prosecuted.