Complex sentence: The truck's passenger was killed, but the driver managed to escape in an accompanying pickup truck; when the tanker truck was evaluated to be engaged in clandestine smuggling, the driver was not considered to pose a security threat to the mission.
Split into simpler sentences: The truck's passenger was killed, but the driver managed to escape in an accompanying pickup truck. As the tanker truck was evaluated to be engaged in clandestine smuggling, the driver was not considered to pose a security threat to the mission.