NORTH MIAMI BEACH, Fla. -- Authorities believe a Miami police detective who was found fatally shot inside a car in North Miami Beach early Tuesday morning returned gunfire before he was killed, Local 10 has learned.

Detective James Walker's body was found in an unmarked vehicle in an alleyway a block away from 1801 NE 164th St. The vehicle was riddled with bullets, Miami police Lt. Bill Schwartz said.

A spent shell casing was found in Walker's car and his gun was out of its holster, Local 10 has learned. Two people are being questioned in connection with Walker's death, but they are not considered suspects at this time.

Walker, 30, was a detective with the Miami Police Department's domestic violence unit. He had been with the department since 2000.

Schwartz said Walker was off-duty at the time of the shooting.

"We have a lot more questions than answers," Schwartz said.

Schwartz said Walker got off work at 11 p.m. Monday. About 12:50 a.m., nearby Miami-Dade and North Miami Beach police heard shots being fired and found Walker dead, Schwartz said.

Residents at a nearby apartment complex told Local 10 they heard multiple gunshots, and one woman said she saw three men running from the complex.

Local 10 has learned Walker was visiting his ex-wife, who lives in the area.

Police recovered a high-powered assault rifle at the crime scene. Schwartz said the search for Walker's killer or killers "is going to be a full-court press."

Schwartz indicated there might be more than one person shot because there were blood trails leading in several different directions. Shortly after noon, police confirmed that one man had been shot in the arm and taken to the hospital. He has since been released and is being interviewed by police, but it was unclear if he was involved in the shooting or just an innocent bystander.

"We're talking to him now to determine what, if any, culpability he has in this matter," Schwartz said.

It was also unclear if Walker was able to return gunfire, but police said it is a possibility.

Schwartz said he thought whomever shot Walker likely knew he was a police officer.

"I think most people aren't fooled by our quote-unquote unmarked cars and, yes, it did have the yellow city (license) tag on it," Schwartz said.

Police have been searching for a white Ford Taurus (2001 or later-model) with right rear-end damage and numerous bullet holes. The vehicle was similar to the one in which Walker's body was found.

Walker's body was taken from the scene in a Miami fire-rescue vehicle. A motorcade of officers escorted his body to the Medical Examiner's Office.