A San Diego (Calif.) Police officer who was shot by a suspect while sitting in his cruiser at a stop sign has died from the shotgun wound he sustained.

Officer Jeremy Henwood, 36, was patrolling a neighborhood in blue-collar City Heights on Saturday at about 5:30 p.m. The driver of a black Audi signaled with his lights, apparently to draw the officer's attention. The driver — identified as Dejon Marquee White, 23, — then pulled alongside the cruiser, lowered the front passenger-side window, leveled a shotgun and fired, striking the officer's head.

Citizens attempted to give first-aid to the officer, and used his radio to call for help, reports NBC San Diego .

About half an hour later, police tracked the Audi to an apartment three blocks away, where officers exchanged gunfire with White, killing him. SWAT officers arrived and surrounded the apartment, where they believed a second suspect was holed up. After two hours, tactical officers entered the apartment to find it empty.

Prior to killing Officer Henwood, White shot a man at an In-N-Out Burger restaurant in El Cajon. Police said he left a rambling two-page suicide note that didn't describe how he planned to kill himself, reports the Associated Press . A misdemeanor arrest warrant had been issued for White for failure to pay a bus or trolley fare, reports NBC San Diego .

Officer Henwood, a four-year veteran, was a captain in the U.S. Marine Corps Reserves. He had recently returned from a yearlong deployment in Afghanistan. 

Sources: Los Angeles Times , San Diego Union-Tribune , and  Associated Press