A DEA agent was killed and another critically wounded Monday morning in a shootout aboard an Amtrak train stopped in downtown Tucson.

One suspect was killed and another is in custody, according to a source who asked not to be named, Tucson.com reports.

Tucson Police Chief Chris Magnus said the shooting suspect was found dead on the train and a second suspect was taken into custody.

Magnus said it started around 8 a.m. when the Counter Narcotics Alliance boarded the train to do a routine check for money, drugs and firearms.

He said CNA made contact with two individuals on the second level of the double-decker train. One suspect was taken into custody while the second, a Hispanic male in his 20s or 30s, pulled out a firearm and started shooting.

A TPD officer was also injured in the shooting after rushing to the train to help when he heard the shots. Magnus said the officer is in stable condition and is expected to survive, KOLD reports.

The suspect was later found dead after barricading himself in a bathroom on the train. Magnus did not know if the suspect was shot by agents or if he took his own life.

There are no reported injuries to those who were onboard, according to an Amtrak spokesperson who said the company is in contact with local and federal authorities about the incident.