A Tennessee couple found transporting millions of dollars’ worth of cocaine was killed in Texas on Thursday during a traffic stop shootout with law enforcement, authorities said.

Edward and Elizabeth Stevenson were first identified through undercover buys of illegal drugs, the Putnam County Sheriff’s Office said Monday.

The undercover work allowed investigators to get a search warrant for the Stevensons’ home, where detectives uncovered nearly a pound of suspected methamphetamine, suspected fentanyl, multiple firearms, body armor and ammunition on Thursday, the sheriff’s office said.