The shooting occurred at the Glenn M. Anderson Federal Building at 501 W. Ocean Blvd. in downtown Long Beach just before 6 p.m. Thursday.
Representatives from the FBI, ICE Homeland Security Investigations and the Long Beach Police Department held a news conference shortly after 10 p.m. Thursday to give details about the shooting.
Steven Martinez, the assistant director in charge of the Los Angeles FBI Office, described the events of the shooting.
Martinez said the shooting was an "incident of workplace violence" between two agents in their workplace. One agent fired several rounds at another agent, striking him. A third agent intervened and fired at the shooter, killing him.
The agent hit by the first gunshots was hospitalized and was listed Thursday night in stable condition.
Martinez said the shooter was believed to have been acting alone.
Long Beach Police received a report of shots fired at the federal building, located at Ocean and Magnolia. Officers responded within two minutes, locked down the building and secured the area.
Long Beach Police Deputy Chief Robert Luna said the FBI would be the lead agency in the investigation, with assistance from Long Beach Police.
The agents involved in Thursday's incident were not identified pending notification of kin.
Earlier in the evening, ICE released a statement:
"At approximately 5:30 (Pacific) this afternoon, two agents with U.S. Immigration and Customs Enforcement's (ICE) Homeland Security Investigations (HSI) were shot inside the agency's offices at the federal building in Long Beach. One of the agents died at the scene. The second agent was transported to a local hospital where he is listed in stable condition. The names of the agents are not being released pending notification of the next of kin. The shooting is being investigated by ICE's Office of Professional Responsibility, the Long Beach Police Department and the FBI."