Sixteen migrants were found inside of a refrigerated tractor trailer at the Interstate 19 immigration checkpoint, just north of Tubac, Thursday.

The temperature was set to 50 degrees, according to a social media post from John R. Modlin, Chief Patrol Agent of the U.S. Border Patrol’s Tucson Sector. It was locked with no means of escape.

The driver of the truck, a U.S. Citizen, faces criminal charges, the post said.