VIENNA (AP) - An Austrian undercover police officer has pleaded not guilty to assaulting an American teacher from Florida after mistaking him for an African drug dealer at a subway station in Vienna.

But his lawyer Bernd Gahler acknowledged that he made mistakes and used force during the Feb. 11, 2009, incident that injured Mike Brennan, a former football player from Jacksonville, Fla.

Thursday's court proceedings follow a previous trial in June that ended with the judge saying the matter was too serious to be handled by her court.

It was unclear when a verdict would be issued. If convicted, the police officer - who cannot be identified under Austrian law - faces up to three years in prison.