The officer was fired on at point-blank range. The vest helped absorb the first bullet.
"Figuring where the heart is ... he's very lucky. Absolutely it saved his life," said Fullerton Police Sgt. Jeff Stuart.
The 32-year-old officer was not identified. He was allegedly shot by 29-year-old Marcos Bush as the officer approached Bush's car during a stop for a minor traffic violation early Sunday morning in Fullerton.
"He exercised all the tactics that he had been trained to do," said Stuart "This was just one of those things that no matter how much you train for, it could still happen."
Police say the officer was shot several times in the upper body and the leg.
"He was able to shoot a couple of rounds back at the vehicle as it took off," said Stuart.
Two hours later, California Highway Patrol officers stopped the suspect's car in Riverside and arrested 27-year-old Sjanee Duhart, suspected of being a passenger during the shooting.
Police say several hours later information led them to a home in Anaheim, where they found Bush. Investigators say Bush took off running.
"He was seen removing a firearm from his waistband, a handgun, and tossing that, discarding it away," said Stuart.
Police arrested Bush, who has a long criminal history. Less than two weeks ago he was found not guilty of charges of carjacking, robbery and attempted murder.
Forensics experts were comparing bullets from the scene with the gun allegedly discarded by Bush.
"We just wish him well, and just keep on training, and speedy recovery, and we just hope he gets back on the job," said retired LAPD officer Alan Edwards as he dropped off flowers for the injured officer.
The officer will celebrate his eighth anniversary with the department next month.
Bush is a known gang member with a lengthy criminal record. He is facing charges including attempted murder of a police officer. Duhart is charged with being an accessory to the crime.
The shooting happened shortly after midnight Sunday at Woods and Knepp avenues located just north of the 91 Freeway. Police say the officer was shot as he approached a dark-colored Pontiac Grand Prix. The wounded officer then to return fire.