VIDEO: DEA agent, gunman killed in Amtrak train shooting in Arizona

A Drug Enforcement Administration special agent was killed Monday when a passenger, who also died, opened fire as officers were doing a routine inspection for illegal contraband on an Amtrak train in Tucson, Arizona, authorities said.

A second agent and a Tucson police officer were wounded.

"It’s very horrific and we’re all just coming to terms with just how terrible a loss this is,” Tucson Police Chief Chris Magnus said. "But I also want to reflect on the really heroic actions of the officers at the scene. They literally ran towards the danger, into the car, where there was an active shooting situation going on.”

Magnus spoke outside the hospital where the wounded agent and Tucson officer had been taken. The agent was listed in critical condition while the officer was in stable condition. He said authorities would not be releasing their names.

The FBI has taken over the investigation of the shooting, which sent passengers fleeing. It happened just after 8 a.m. on a train stopped at the station in the city's downtown. A regional task force of DEA agents and Tucson police officers had boarded one of the cars to do a typical check for illegal money, weapons and drugs. It's a common occurrence at all transit hubs, Magnus said.

Officers were in the middle of detaining a man on the upper level of the double-decker car when a second man pulled out a handgun and began firing. He exchanged several rounds with police and then barricaded himself in a bathroom on the lower level, Magnus said.

He was later found dead inside.

Associated Press