FRANKFURT -- German prosecutors have opened a criminal investigation against WBA super middleweight champion Felix Sturm because of doping.

Cologne prosecutor Daniel Vollmert says Sturm is suspected of violating Germany's new anti-doping law and could face up to three years in prison if convicted.

Sturm tested positive for the anabolic steroid stanozolol after his split decision victory over Fedor Chudinov on Feb. 20 in Oberhausen, Germany. He has denied any wrongdoing.

Sturm won the fight against the previously unbeaten Chudinov on the cards of two judges, while one ruled it a draw. Many fans felt Sturm had been the inferior fighter.

His victory made him the first German to be a world champion five times, having also held the WBA and WBO middleweight titles. He has moved back to his native Bosnia.