Seventeen people were found dead when authorities opened up a sweltering, airless trailer abandoned at a South Texas truck stop with more than 100 illegal immigrants locked inside.
An 18th victim died later Wednesday at a hospital in one of the deadliest smuggling attempts on record in the US.
The men, women and children from Mexico, El Salvador, Guatemala and Honduras were apparently so desperate for air that they tried to claw through insulation on the back door. At least one of those trapped inside placed a desperate call to police late Tuesday, saying people were suffocating and pleading with a dispatcher to "help me."
When sheriff's deputies opened the trailer at about 2am, "a flood of human beings" spilled out, US attorney Michael Shelby said. Many ran off, but others were too weak to go far.
Thirteen bodies were found inside the trailer and four more on the ground just outside. A five or six-year-old boy was among the dead.
Authorities said one of three suspected smugglers was arrested Wednesday in the Houston area, about 185km northeast of Victoria. The man, one Tyrone Williams of New York, was not immediately charged.
The trailer is registered in Williams' name and had New York plates, Shelby said. Authorities were still looking for two more suspects whose names were not released.
The smugglers apparently unhitched the trailer at the truck stop near Victoria, about 281km from the Mexican border, and drove off. Insulation around several small holes in the back door was scraped away, suggesting the immigrants had tried to get out.
Someone inside the trailer also telephoned authorities, pleading for help. The 911 call to police in Kingsville, 160km south of Victoria, came in just before midnight Tuesday from a Spanish speaker on a cellular phone with lots of yelling and background noise.
Police Chief Sam Granato said the call was cut off and the number couldn't be traced. But after listening to a digital recording, Granato said police were able to hear the man saying that people were asphyxiating.
Granato said someone traveling on US Highway 77 called police to report seeing a hand waving a bandanna out of a hole in the back of a white 18-wheeler truck with New York plates at a truck stop.
It was the deadliest immigrant-smuggling attempt in the US in more than 15 years. In 1987, the Border Patrol found 18 Mexican immigrants dead in a boxcar left on a rail siding in the West Texas town of Sierra Blanca.
Mexican President Vicente Fox's office issued a statement mourning the deaths and expressing his condolences to the victims' families.