Houston ? The driver of the tractor-trailer that became a sweltering deathtrap for 18 people was charged Thursday with transporting and harboring illegal immigrants, and authorities searched for three more suspects in one of the deadliest smuggling schemes in U.S. history.

The driver, Tyrone Williams of Schenectady, N.Y., at first told authorities he thought his trailer was empty, then admitted he was paid $2,500 by two men to take 16 immigrants from the Mexican border into south Texas, according to court papers.

He claimed he did not watch as the immigrants were loaded into his trailer Tuesday night, though he could feel the truck rocking as he sat in the cab.

The trailer was actually packed with 100 men, women and children from Mexico and Central America.

Seventeen died inside and another at a hospital in Victoria, where the trailer was discovered abandoned early Wednesday. It was the deadliest immigrant-smuggling scheme in the United States in at least 16 years.

Williams, 32, claimed he threw open the doors after discovering the dead and dying immigrants inside, then drove off. Authorities, however, said the doors had to be opened by sheriff’s deputies.

Eduardo Ibarrola, Mexico’s consul general in Houston who has interviewed some of the survivors, said the immigrants crossed the border in different ways before gathering in Harlingen, at the southern tip of Texas, for a 300-mile ride on U.S. Highway 77 to Houston.

He said they were loaded into the trailer around 10 p.m. Tuesday and were surprised at how crowded it was. He said there was no water, no light and not nearly enough air.

“They didn’t realize the danger of the situation,” Ibarrola said. “They realized (too late) that there were so many people, that there was no air and that they could not get out.”

Lourdes Cano cries and holds her 8-month-old baby Thursday in Pozos, Mexico, as she hears the news that her brother-in-law died at a Texas truck stop after being locked inside a sweltering semitrailer in an attempt to sneak to Florida to work at a tomato packing plant. Eighteen illegal immigrants died from suffocation and heat exhaustion early Wednesday in and near a truck parked at a Texas highway rest stop not far from the city of Victoria, an emergency services official said.

The immigrants were found about four hours later at a truck stop near Victoria.

Authorities said they were still looking for “Joe,” “Abel” and “Fatima” in the smuggling scheme.

All four suspects could get life in prison, perhaps even the death penalty, federal prosecutor Don DeGabrielle said.

Williams was arrested Wednesday in the Houston area, hours after the grim discovery in his trailer 115 miles away.

He did not enter a plea to the federal charges and remains jailed pending a bond hearing. He did not yet have an attorney.

According to court papers filed by investigators, Williams said he felt “shock, fear and confusion” after he discovered the immigrants gasping for air.

He said he unhitched the trailer at the truck stop and then drove to a Houston hospital, where he initially told authorities he had thought the trailer was empty. It is not clear why he went to the hospital.

After authorities talked with a survivor, Williams changed his story and admitted finding the immigrants.