Federal authorities are investigating the fatal shooting of an 18-year-old Eagle Pass drug suspect, allegedly by a U.S. Border Patrol agent.

Maverick County Sheriff Tomas S. Herrera said Friday deputies found no evidence Juan Mendez of Eagle Pass was armed when he was shot. The agent’s identity hasn’t been released.

Herrera says the agent stopped a truck Mendez was driving Tuesday and began to question him. Witnesses say a 15-year-old boy fled the truck, and Mendez struggled with the agent, broke free and was shot twice. Herrera says Mendez was taken to Fort Duncan Medical Center in Eagle Pass, where he died. The passenger is in juvenile custody.

Herrera says 325 pounds of marijuana were found in the truck.

A spokeswoman for U.S. Customs and Border Protection had no comment.