Moscow (CNN) Russian law enforcement agencies are questioning a prominent historian over the death of a former student in the city of St. Petersburg, in a case that has grabbed headlines across the country.

Investigators opened a criminal case after the man was pulled out of the Moika River, a waterway in the heart of the historic city, early Saturday morning.

The Investigative Committee, Russia's top law-enforcement agency, said in a statement that a pair of severed arms and a nonlethal handgun were discovered in a backpack the man was carrying, and that he had been detained as a suspect.

The suspect in the case is an academic celebrity. Russian state news agencies identified him as Oleg Sokolov, a professor at St. Petersburg State University. He is currently being treated for hypothermia in hospital.

Sokolov was arrested after being pulled out of the Moika River in St. Petersburg.

According to his university biography , Sokolov is a specialist in the military history of France and a professor at the university's Department of Modern and Contemporary History.

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