Updated

Sheriff's deputies found 56 illegal immigrants locked inside a refrigerated trailer with no driver in sight and no way for the shivering human cargo to escape. Two suspected immigrant smugglers from Mexico later were arrested.

An anonymous call led deputies to the trailer in a warehouse district of Laredo. The key was in the ignition and the trailer's refrigeration was on, Webb County Sheriff Rick Flores said.

The 43 men, 11 women and two children had been in the truck for about six hours, Flores said. None was injured, but when deputies found them, they were bunched together in the center of the trailer to avoid the icy walls and to try to stay warm.

"They couldn't get out of there even if they had wanted to," said Melanie Velarde of Crime Stoppers in Laredo. "The walls of the truck were sealed shut to keep the cold in, and the doors were locked and bar-shut from the outside."

Flores said the people had been loaded into the trailer on the American side of the border. The smugglers may have had trouble finding a driver, he said.

The suspected smugglers, a man and woman, were arrested late Wednesday at a house in Laredo near Interstate 35. Investigators suspect the house was being used as a staging location for human smuggling, said Nina Pruneda, spokeswoman for the U.S. Department of Immigration and Customs Enforcement in San Antonio.

The two, believed to be illegal immigrants themselves, were held on suspicion of harboring illegal immigrants and were scheduled to face a U.S magistrate in Laredo on Friday, Pruneda said. Their identities were not released and additional charges and arrests were possible, she said.

Most of the immigrants had been returned to Mexico by Wednesday evening, Pruneda said.