Florida ? A Miami city police officer was found shot to death in his unmarked patrol car early Tuesday, authorities said.

Detective James Walker, 30, was found in an alley by North Miami Beach officers responding to reports of shots fired around 12:30 a.m., said Miami police spokesman Lt. Bill Schwartz. It wasn’t known if Walker returned fire, he said.

Police were searching for a suspect in a white Ford Taurus with bullet holes, but they didn’t release details on the gunman. Blood trails led from Walker’s car, and a high-powered rifle was found at the scene. Schwartz declined to say whether it was used to kill Walker.

“His car had been filled with holes,” Schwartz said.

One man being questioned had been shot in the arm Tuesday morning, but police did not call him a suspect. “He might just be an innocent bystander,” Schwartz said.

Walker had been a member of the Miami police since 2000 and was working with the domestic violence unit. He went off duty around 11 p.m. Monday, and it’s not clear what he was doing in North Miami Beach.

Walker’s ex-wife lived in the area where he was found, said John Randle, the detective’s brother-in-law.