A DEA agent was killed, another was wounded along with a Tucson police officer in a gunfight Monday morning aboard an Amtrak train that stopped in Tucson, officials say. Meanwhile, Tucson police say, one suspect was killed and another is in custody.Β It occurred during a drug operation involving the Counter Narcotics Interdiction squad, a multi-agency group that often conducts routine drug sweeps on trains and other transportation facilities.