By RALPH BLUMENTHAL
 
HOUSTON, Mar. 12 - Scott Reuter, an Army reservist working in a South Texas restaurant, was driving home one warm May night two years ago when something about a white tractor-trailer ahead of him on Highway 77 caught his eye.

A taillight was dangling out of its socket. But as Mr. Reuter drew closer, he saw something else: sticking through the hole was a hand. It was wrapped around the light, waving it. Underneath, he saw another empty light hole. Another hand was sticking out of that, waving a bandanna.

"The hand holding the bandanna," he testified in federal court here last week, "looked very frantic to me."

Mr. Reuter sped up to pass, hoping to catch the driver's eye, but it was too dark outside and too dark in the truck's cab. Noting the license number, he reached for his cellphone to dial 911. The battery was dead. He called from a pay phone later, but by then the truck was long gone.

The 18-wheeler, which had been packed in Harlingen, Tex., with at least 74 illegal immigrants from Mexico, Central and South America, drove on to its rendezvous with death: 19 of its hidden riders fell victim to suffocation, broiling heat and dehydration in the nation's deadliest human smuggling disaster.

The truck, a sealed refrigeration unit with the air turned off, was found abandoned in Victoria, Tex., on May 14, 2003. It was not the only moment in which the fates seemed to conspire against the passengers, witnesses testified at the trial of the truck driver, Tyrone M. Williams, 34, a Jamaican immigrant from Schenectady, N.Y. He is the only defendant of 14 who faces possible execution if convicted. Some have pleaded guilty, and face up to life in prison.

Two smugglers who were to reload the immigrants into a pickup truck and a van once the 18-wheeler was past a Border Patrol checkpoint in Sarita, Tex., were themselves detained there. Without the promised relief vehicles, the passengers stayed in the scorching truck for what became a journey of about two extra hours toward Houston.

And when one of the riders used a cellphone that his worried mother had slipped him before the trip, his first call to 911 reached an operator who seemed to speak no Spanish and his next call lost the connection after a few seconds.

In often gripping detail, the opening week of what is expected to be a six- to eight-week trial before a jury of seven women and five men offered conflicting testimony on the degree of Mr. Williams's culpability. The same accounts that portrayed Mr. Williams as cruelly indifferent to the agonies of his passengers were offered as evidence that he was unaware of their suffering.

Again and again, the assistant United States attorneys, Daniel C. Rodriguez and Stacy de la Torre, elicited testimony from tearful survivors that the driver was to blame for their anguish. But Mr. Williams's lawyer, Craig Washington, in his opening statement and cross-examination of witnesses, suggested that veteran organizers of the smuggling ring - who were paid by the head, while Mr. Williams received a flat fee of $7,500 - overloaded the truck to maximize their profit and that they were the ones who locked the passengers in, while the driver remained behind the wheel, never hearing their later cries.

After an admitted conspirator who pleaded guilty to recruiting Mr. Williams testified that the trucker had smuggled 60 illegal immigrants on a shorter route without incident two weeks earlier, the question remained why the air in the truck proved so disastrously insufficient the second time. A medical examiner who performed autopsies on the bodies said more people would have used up the air faster.

There were 55 survivors, along with the 17 dead in the truck and 2 more who died later, for a total of 74 known immigrants. But once Mr. Williams opened the truck doors in Victoria before fleeing in the cab with a woman who had accompanied him to carry out a drug deal, as the investigation established, some other survivors appear to have scattered, leaving open the question of whether many more than 74 had been inside.

Some of the most emotional testimony came from a Honduran man, Matías Rafael Medina Flores, who said the two calls to 911 on his cellphone from inside the truck failed to summon help. After a fellow rider punched out the taillights for air, he said, "We would take turns to get to the holes so we could breathe." They made sure, he said, to give the first chance for air to the youngest passenger, a 5-year-old boy.

The child, the Honduran man testified, died in the hour or more they took to reach the Sarita checkpoint. There, he said, passengers screamed to attract the attention of inspectors. But other witnesses contradicted his account, insisting that they still had hope of sneaking through and enforced a communal silence at the checkpoint. That would accord with the testimony of an inspector who said he had no reason to suspect a hidden human cargo.

A surveillance videotape from a convenience store and gas station in Victoria where the truck came to rest about 1:30 a.m. on May 14 offered the jury a striking record of the actions of Mr. Williams and his riding companion that it could interpret in various ways.

With the dead piled behind locked doors in the truck parked outside, the tape shows Mr. Williams entering the store and asking the clerk, Eloy Garcia: "Do you all carry water? Hey, General, that is what I need. Ha ya ya!" He collected armfuls of water bottles, asking, "Hey, General, what is the name of this town?" Mr. Williams paid for the bottles and returned for more. "How much are these potato things?" he asked.

The bill for an armful of chips and water came to $20.79, and Mr. Williams counted out the exact change. He came back twice more, for more water.

Then the tape shows the woman who was traveling with him, Fatima Holloway, entering the store. "Where's your restroom?" she asked. Then she also bought water, asking the price and sounding pleased to hear it was on special, 50 cents a bottle. Together she and Mr. Williams bought 55 bottles, which survivors later testified were handed to them through holes in the truck.

Ms. Holloway was still inside the store. "Can I ask you a question?" she said to Mr. Garcia. "Are there rattlesnakes out here?"

"Oh, yeah," he said.

She appeared to be asking because outside Mr. Williams had opened the truck doors and survivors were fleeing. The tape shows one of them, a shirtless, apparently delirious man, later identified as Nelson Fernandez, bursting into the store.

"911!" he shouted. "They tried to kill -- " he began.

"Who?" Mr. Garcia asked.

Mr. Fernandez rambled. "I am thirsty. Water," he said.

Then, with Ms. Holloway looking on, Mr. Garcia called the police. "I've got a fellow that just came in saying that he's got some people after him, that want to kill him," he said.