A man shot a police officer to death Thursday following a traffic stop in suburban Atlanta (search), then ran inside a post office and apparently killed himself, authorities said.

A witness said the gunman was holding the officer hostage in front of the building when he shot him at point-blank range. The gunman and another officer exchanged fire before the gunman fled into the post office, and it was surrounded by police.

All four postal employees managed to escape through the back of the building, and it was not immediately known if any customers were inside at the time, said Paul Krenn, a spokesman for the U.S. Postal Inspection Service (search).

The slain officer worked for the police department in the Atlanta suburb of Pine Lake (search), DeKalb County Police Chief Louis Graham said.

The gunman died of what appeared to be a self-inflicted gunshot wound, Krenn said.

The police chief confirmed that the confrontation stemmed from a traffic stop, but details were not immediately available.

Witness Susan Boozer said the violence was unfolding as she drove up to the post office. She saw two officers near a parked blue SUV, one with his gun drawn. A man had his arm around the chest of one of the officers and was shouting at the other: "'Go on and shoot. Go on and shoot,'" she said.

The man then shot at the officer who was pointing the gun at him, and then he shot the one he was holding, Boozer said.

Gunfire ensued between the man and the other officer. Boozer guessed that about 10 shots were fired before the man entered the post office.