LONG BEACH, Calif.  >> A federal immigration agent killed a colleague who had shot a high-ranking official six times while being counseled on his job performance inside an Immigration and Customs Enforcement office, the FBI said Friday.

Authorities identified the gunman in the Thursday evening attack as supervisory special agent Ezequiel Garcia, 45, and the victim as Kevin Kozak, 51, deputy special agent in charge of the Los Angeles area.

Garcia was killed by an unidentified agent who intervened after Kozak was shot. Kozak was in stable condition at a hospital and was described as alert and talking.

"He is a fighter and I believe that’s why he’s alive today," said Claude Arnold, ICE special agent in charge. "He refused to succumb to his injuries and in law enforcement that’s what makes the difference between people who go home at the end of the day and those who don’t."

Arnold said he wasn’t aware of any issues between Garcia and Kozak.

"We are doing everything humanly possible to understand why it happened and to ensure it will not happen again," he said.

Such a shooting among agents was unprecedented in the department’s history, Arnold said.

It occurred just before 6 p.m. Thursday on the seventh floor of the Glenn M. Anderson Federal Building in Long Beach, about 20 miles south of downtown Los Angeles.

The third agent, who wasn’t injured, was placed on administrative leave and his identity was withheld.

However, a federal official with knowledge of the investigation told The Associated Press that Kozak, the second in command of the Los Angeles area, had denied a request for an internal transfer request by Garcia. The official wasn’t authorized to speak publicly but agreed to speak on condition of anonymity.

Kozak has served in his current role since 2004 and has worked as a civil servant for nearly 30 years.

Garcia initially worked for the now defunct Immigration and Naturalization Service and was promoted to supervisor within ICE in 2004.

He was a plaintiff in lawsuit against the Los Angeles Police Department after he and another ICE agent claimed they were roughed up by five officers while doing undercover work. A federal jury found in the police officers’ favor in 2005, saying they didn’t use excessive force against Garcia and the other agent.

The Long Beach federal building houses ICE, the Internal Revenue Service and the U.S. Probation and Parole Office.

Along with the FBI, the shooting was being investigated by ICE’s Office of Professional Responsibility and Long Beach police.

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Associated Press writer Shaya Tayefe Mohajer contributed to this report.