A 26-year-old man has been convicted of involuntary manslaughter in the killing of an off-duty Baltimore police officer last year.

A jury found Sian James guilty of the charge Monday for hurling a piece of concrete at Detective Brian Stevenson’s head during a dispute over a parking spot in Canton in October. The concrete chunk fractured Stevenson’s skull.

Prosecutors said James ratcheted up an argument into a deadly assault. James testified last week that he acted in self-defense and feared Stevenson was going to shoot him and his friend.

James had faced charges of first- and second-degree murder, voluntary manslaughter and carrying a dangerous weapon in the case.

He faces a maximum penalty of 10 years at his sentencing in July.