Authorities rescued 56 illegal immigrants this week after finding them huddled inside a refrigerated trailer with no way to get out.
An Immigration and Customs Enforcement spokeswoman says none of the immigrants were injured and most had been returned to Mexico by last night.
One of the immigrants was Brazilian.
Acting on a tip, Webb County Sheriff Rick Flores says deputies found the truck on Tuesday with the key in the ignition and the trailer's refrigeration on.
The immigrants included 43 men, 11 women and two children. They had been in the truck for about six hours.
Flores says they were bunched together in the center of the trailer to avoid the icy walls.
The immigrants had been loaded into the trailer on the American side of the border after crossing the Rio Grande River, he says.
No arrests had been made as of yesterday.
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