Our condolences to the San Antonio Police Department. https://t.co/7XJY95SpX1 — VA Chiefs of Police (@vachiefs) November 20, 2016

A San Antonio police detective was shot dead in his squad car on Sunday as he was writing a traffic ticket, and a suspect is still at large, the department’s police chief said.

Chief William McManus said during a press conference that Detective Benjamin Marconi, 50, had stopped a vehicle for a traffic violation when another vehicle drove up behind his squad car, approached the window of the police car and shot him in the head, the Associated Press reported.

“This is everyone’s worst nightmare,” McManus said.

The suspect also shot Marconi a second time before leaving the scene. Marconi was a member of the department for 20 years. The incident took place about 11:45 a.m. local time, McManus said. Marconi was pronounced dead at a hospital, according to the AP.

A motive for the shooting is unknown.