The Immigration and Customs Enforcement agents were shot on the seventh floor of the Glenn M. Anderson Federal Building in Long Beach, about 20 miles south of downtown Los Angeles.
The 5:54 p.m. Thursday shootings were described by the FBI's Steven Martinez as a case of "workplace violence involving two federal agents in their office space." He offered no other details about what led to the initial shooting.
But the Los Angeles Times, citing multiple law enforcement sources, reported Friday that the initial shots were fired by an agent at his supervisor during an unspecified dispute.
"Another agent, working nearby, intervened and fired his weapon to prevent additional rounds being fired at the victim," said Martinez, the assistant director in charge of the FBI's Los Angeles office.
The gunman died at the scene and the wounded agent was hospitalized at St. Mary Medical Center. ICE Special Agent in Charge Claude Arnold would only say he was stable.
St. Mary's hospital trauma director James Murray told KCAL-TV that the injured agent had multiple gunshot wounds, but he didn't give details. The victim's vital signs were "good for now," Murray said.
The names of the dead gunman, the victim and the agent who fired the final rounds were not released.
There were conflicting early reports about the number of people shot, with local authorities saying two were dead and one wounded, while ICE said one was dead and one wounded.
The Long Beach federal building houses ICE, the Internal Revenue Service and the U.S. Probation and Parole Office.
"At times like this, words honestly seem inadequate. When something like this happens in our offices, it's incomprehensible," Arnold said.
Along with the FBI, the shooting was being investigated by ICE's Office of Professional Responsibility and Long Beach police.
