Fulton County Police officer Terence Green, 48, was killed Wednesday in Fairburn, Georgia.
A second officer was shot in the hip, but suffered no injuries.
"It was actually his radio -- the bullet went through -- the radio saved him. It penetrated the radio," said Fulton Police Chief Cassandra Jones.
The incident occurred when police were searching a neighborhood after reports of gunfire from the home of Amanuel Menghesha, 42.
Menghesha allegedly fired at the officers without warning, authorities said. He "appeared to have gone on a rampage," said Fulton County Assistant Chief Gary Stiles, who described it as an "ambush."
Police said the officers were shot with an "assault style rifle." Menghesha was then shot by other officers.
Green was shot in the head and died at a local hospital. The suspect was transported to the same hospital, but his injuries do not appear to be life threatening. Charges are pending.
The suspect was known to police, and had "violent tendencies," Jones said.
Police say weather and poor visibility also played a factor. There was dense fog in the area at the time of the incident.
"This is a call that I pray every night, every day, 10 times a day that I never get. And when you get it, you're not ready for it, but you have to lead and you have to go on because you have to stand there and be that strength for your officers, but it's one that you just can't even imagine," Jones said in a news conference.
"It's like losing a child because they're all my children."
Green, a 22 year veteran of the police force, is survived by his parents, brother and four sons.