Story highlights ICE Director John Morton is headed to Long Beach, California

The federal building has reopened to the public

FBI official says it looks like an isolated incident

"The situation began ... as an incidence of workplace violence," FBI official says

A dispute between federal immigration agents that left one of them dead and another injured in southern California prompted the head of the Immigration and Customs Enforcement agency to travel to the scene on Friday.

Federal officials said the incident occurred during a counseling session regarding performance.

Director John Morton traveled to Long Beach, where the confrontation occurred Thursday evening,

"The situation began ... as an incidence of workplace violence involving two federal agents in their office space," said Steven Martinez, assistant director of the FBI office in Los Angeles. "When the incident escalated, one agent fired several rounds at the other agent, wounding him."

A third colleague intervened and fired at the shooter, killing him, Martinez said.

Kevin Kozak, 51, a deputy special agent in the Los Angeles area, suffered multiple injuries and is undergoing treatment at a hospital. He is in stable condition.

Federal agent Ezequiel Garcia, 45, was killed during the incident.

"At this time, we believe this is an isolated incident and we believe the shooter was acting alone," Martinez said.

The investigation includes officers from the ICE, the Long Beach Police Department and the FBI.

By Friday morning, the federal building had reopened to the public, said FBI spokeswoman Laura Eimiller.