Police later found the decapitated head of the student in Oleg Sokolov's apartment and he's been arrested on suspicion of murder.
Solokov is now in hospital suffering from hypothermia.
The history professor and his student were said to be in a relationship and police say Solokov claims he 'accidentally' killed her on Thursday her during an argument. He then had guests come for a dinner party on Friday while her body laid in his apartment.
The professor was reportedly drunk when he went into the Moika River in St Petersburg, Russia, in the early hours of Saturday morning. After being dragged from the river police found two severed arms in his rucksack, along with a gun, and then later made the gruesome discovery in his apartment.
Police divers have been seen scouring the river, possibly searching for more body parts.
Solokov is a leading expert in military history and also enjoys historical re-enactments where he has previously dressed as Napoleon.
He has worked with European television broadcasters as an expert adviser on films depicting the Napoleonic era, and he was made a knight of the Legion of Honour in France in 2003.