A man who authorities initially said was fatally shot last month was actually killed when he was struck by a rock during a struggle with a robbery victim acting in self-defense, Prince George’s County police said.

Tauron Williamson, 23, of Oxon Hill and Tyron Wheeler, 22, of Northeast Washington were trying to rob two men in Landover, Md., on April 22 around 9 p.m., police said Friday. One of the victims was shot by Wheeler, and the second one fought back, hitting Williamson on the head with a rock, police said.

Williamson died two days later. The man who was shot remains in critical condition, police said.

An initial medical observation suggested Williamson died of a gunshot wound, but detectives later learned through an autopsy that his fatal injury came from a blow to his head, police said.

Williamson and Wheeler did not know the men they were robbing, Prince George’s police spokesman Nicholas Clayton said.

Wheeler has been charged with attempted murder, armed robbery and other offenses, police said. He is being held in jail without bond. His attorney could not be immediately reached for comment.