Texas state police say the trooper who fired from a helicopter at a pickup truck carrying illegal immigrants was trying to disable the speeding vehicle.
Two people were killed and two wounded Thursday in the incident on an isolated road along the Mexican border near the town of La Joya, about 70 miles northwest of Brownsville.
Police said Friday that the truck appeared to be carrying "a typical covered drug load" and was travelling at reckless speeds, endangering the public.
The officer who fired on the truck has been placed on administrative leave.
Eight people were arrested, seven of them illegal immigrants from Guatemala. The nationalities of the dead and the other detainee were not released.