San Antonio - The driver of a broiling tractor-trailer found packed with immigrants outside a Walmart in San Antonio was charged on Monday in the deaths of 10 of his passengers and could face the death penalty.James Matthew Bradley jnr, 60, of Clearwater, Florida, awaited an appearance in federal court later in the day to face charges of illegally transporting immigrants for financial gain, resulting in death.Authorities discovered eight bodies inside the crowded 18-wheeler parked in the summer heat, and two more victims died at the hospital. Officials feared the death toll could rise because nearly 20 others rescued from the truck were in dire condition, many suffering from extreme dehydration and heatstroke.A passenger told authorities that they took turns breathing through a hole in the trailer and pounding on the walls to try to get the driver's attention, according to court papers."We're looking at a human-trafficking crime," San Antonio Police Chief William McManus said on Sunday, calling it "a horrific tragedy".Unaware of peopleBradley told investigators that the trailer had been sold and he was transporting it from Iowa to Brownsville, Texas, and that he was unaware that there were people inside until he parked and got out to urinate.After hearing banging and shaking, he opened the door and was "surprised when he was run over by 'Spanish' people and knocked to the ground'," according to the complaint.Bradley allegedly told investigators that he knew the trailer refrigeration system didn't work and that the four ventilation holes were probably clogged. He also said he did not call 911, even though he realised that several people already were dead.A passenger told investigators that he and others crossed the Mexican border into the US illegally by raft and were then guided into the trailer to be taken north to San Antonio, according to the criminal complaint. The passenger said the immigrants inside the truck soon began to struggle breathe.The victims "were very hot to the touch. So these people were in this trailer without any signs of any type of water", Fire Chief Charles Hood said.It was the latest smuggling-by-truck operation to end in tragedy. In one of the worst cases on record in the U.S., 19 immigrants locked inside a stifling rig died in Victoria, Texas, in 2003.More than 100 peopleBased on initial interviews with survivors of the San Antonio case, more than 100 people may have been packed into the back of the truck at one point in its journey, said Thomas Homan, acting director of US Immigration and Customs Enforcement. Officials said 39 people were inside when rescuers arrived, and the rest were believed to have escaped or hitched rides to their next destination.At least some of those in the truck were from Mexico and Guatemala, according to diplomats from the two countries.Latin Americans who enter the US illegally often rely on smuggling networks that use safe houses and various vehicles to help them reach their destination."Even though they have the driver in custody, I can guarantee you there's going to be many more people we're looking for to prosecute," Homan said.The truck had an Iowa license plate and was registered to Pyle Transportation of Schaller, Iowa. A company official did not immediately respond to a phone message seeking comment.San Antonio is about a 240km drive from the Mexican border. The temperature in San Antonio reached 38°C on Saturday and didn't dip below 32°C until after 22:00. VigilThe tragedy came to light after a person from the truck approached a Walmart employee and asked for water late on Saturday night or early Sunday morning, said McManus. The employee gave the person water and then called police.On Sunday evening, about 100 people gathered at a San Antonio church for a vigil to mourn the dead.Immigrants' rights activists and church officials held up handmade signs reading "Who here is not an immigrant" and "No human is illegal."Those gathered held a moment of silence, then gave speeches blaming federal and Texas authorities' hard-line immigration policies for contributing to the deaths by forcing immigrants to take greater risks to reach the US."These tragedies are compounded when it's incredibly dangerous and incredibly expensive and we push migration into the hands of illicit actors," immigration activist Bob Libal said in a telephone interview.In the May 2003 case, the immigrants were being taken from South Texas to Houston. Prosecutors said the driver heard them begging and screaming for their lives, but refused to free them. The driver was sentenced to nearly 34 years in prison.The Border Patrol has reported at least four truck seizures this month in and around Laredo, Texas. On July 7, agents found 72 people crammed into a truck with no means of escape, the agency said. They were from Mexico, Ecuador, Guatemala and El Salvador.Authorities in Mexico have also made a number of similar discoveries over the years.