TUCSON, Ariz. (NewsNation Now) — A Drug Enforcement Administration special agent was killed Monday when a passenger opened fire as officers conducted a routine inspection on a parked Amtrak train in Tucson, Arizona.

The passenger also died. A second DEA agent and Tucson police officer were hurt, The Associated Press reports. The agent was listed in critical condition while the officer was in stable condition.

“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 toward the danger, into the car, where there was an active shooting situation going on.”

The shooting, which sent passengers fleeing, 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.

The other suspect has been arrested. It wasn’t immediately known what charges he faces or his relationship to the second man.

The Associated Press reported it happened just after 8 a.m. Monday. City police tweeted nearly three hours later the scene was secure.

There are no reported injuries to the crew or passengers, said Amtrak spokesman Jason Abrams.

The Sunset Limited, Train 2, was traveling from Los Angeles to New Orleans, and arrived at the Tucson station at 7:40 a.m., Abrams said. There were 137 passengers and 11 crew members, he said. All have been evacuated to the station.

Evan Courtney was on the train and told NewsNation people began yelling “shots fired.” He grabbed his backpack and ran.

“I looked out of the window and saw SWAT with assault rifles huddled behind barricades,” he said. “After about 15 minutes, police ran to us and told us to get out of the car and run in the opposite direction, out of harm’s way.”