A Russian professor was pulled from a river. Police said a woman's arms were found in his rucksack

Russian professor Oleg Sokolov attends a court hearing in Saint Petersburg on November 11, 2019.

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.
    Law enforcement officials told the Russian state news agency RIA-Novosti that the dismembered body of the victim, Anastasia Yeshchenko, a former student of the professor, was found in Sokolov's apartment.
    Yeshchenko came from the southern Russian city of Krasnodar to study in St. Petersburg and had continued to work with Sokolov as a researcher, according to the state news agency TAS