City police said the officer was taken to a hospital with injuries not believed to be life-threatening.
Police also released a photo of a silver sedan that was spotted leaving the area of the courthouse.
City Councilman Sal DiCiccio said in a statement that “multiple shots were fired at the officer who was struck in the vest.”
The officer is court security officer who works for the U.S. Marshall's Service and the officer was expected to recover, said a law enforcement official who spoke on condition of anonymity because the official was not authorized to discuss the investigation publicly.
The shooting came after the weekend ambush of two Los Angeles County deputies who were in their parked police vehicle when a man walked up to the passenger’s side and fired multiple rounds.
The deputies were struck in the head and critically wounded but both are expected to recover. The gunman hasn’t been captured and a motive has not been determined.
DiCiccio said the security officer was shot in front of the Sandra Day O’Connor federal building.
—- Associated Press Writer Michael Balsamo contributed to this report from Washington.