San Antonio - A man will be charged in federal court following his arrest in the deaths of nine people whose "very hot" bodies were found in a sweltering tractor-trailer in a Texas parking lot alongside nearly 20 others who were still alive but in dire condition, federal prosecutors said.Authorities fear the death toll from the grim weekend discovery could rise because many of those hospitalised were suffering from extreme dehydration and heatstroke, officials said Sunday."We're looking at a human-trafficking crime," said San Antonio Police Chief William McManus, calling it "a horrific tragedy".James Mathew Bradley jnr, 60, of Clearwater, Florida, has been taken into custody and will be charged in federal court on Monday, prosecutors said. The US Attorney's Office wouldn't say whether Bradley was the alleged driver of the truck. One US official said on Sunday evening that 17 of those rescued were being treated for injuries that were considered life-threatening. The official spoke to The Associated Press on condition of anonymity because the information has not been publicly released.Authorities were called to the Walmart parking lot in San Antonio late on Saturday or early on Sunday and found eight people dead inside the truck. A ninth victim died at the hospital, said Liz Johnson, spokesperson for US Immigration and Customs Enforcement.No water, airconThe victims "were very hot to the touch. So these people were in this trailer without any signs of any type of water", San Antonio Fire Chief Charles Hood said.Authorities would not say whether the trailer was locked when they arrived, but they said it had no working air conditioning.It was just the latest smuggling-by-truck operation to end in tragedy. In one of the worst cases on record in the US, 19 immigrants locked inside a stifling rig died in Victoria, Texas, in 2003.Based on initial interviews with survivors of the San Antonio tragedy, more than 100 people may have been packed into the back of the 18-wheeler at one point in its journey, ICE acting Director Thomas Homan said. Officials said 39 people were inside when rescuers arrived, and the rest were believed to have escaped or hitched rides to their next destination.Four of the survivors appeared to be between 10 and 17 years old, Homan said. Investigators gave no details on where the rig began its journey or where it was headed.But Homan said it was unlikely the truck was used to carry the immigrants across the border into the United States. He said people from Latin America who rely on smuggling networks typically cross the border on foot and are then picked up by a driver."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.Mexican Consul General in San Antonio Reyna Torres said Mexican nationals were among the survivors and those who died on the rig.The Mexican government also released a statement on Sunday night expressing its condolences to the relatives of those who died and called for an "exhaustive investigation"A Guatemalan official said two natives of Central American country were among those hospitalised. Consul Cristy Andrino in McAllen said the two told her they had crossed into the US on foot and were later picked up by the rig.Guatemala was seeking to obtain witness status for the two survivors so they wouldn't be deported, Andrino said.Brutality The US Homeland Security Department is leading the investigation. Department Secretary John Kelly said the deaths demonstrate the brutality of smuggling organisations that "have no regard for human life and seek only profits".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.The tragedy came to light after a person from the truck approached a Walmart employee and asked for water late on Saturday night or early on Sunday morning, said McManus, the local police chief.The employee gave the person water and then called police, who found the dead and the desperate inside the rig. Some of those in the truck ran into the woods, McManus said.Investigators checked store surveillance video, which showed vehicles arriving and picking up people from the truck, authorities said. Walmart released a brief statement on Sunday saying it was doing what it could to help investigators.On Sunday evening, about 100 people gathered at a San Antonio church for a vigil to mourn those killed.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' embrace of harsher immigration policies for contributing to the deaths.Harsher immigration policiesJonathan Ryan, executive director of a nonprofit called Raices, said it's "an unfortunate example" of what happens when such policies are enacted.A new law approved by the Texas Legislature lets police inquire about peoples' immigration status during routine interactions such as traffic stops.Bob Libal is executive director of Grassroots Leadership, an Austin-based nonprofit that supports more liberal immigration policies."These tragedies are compounded when it's incredibly dangerous and incredibly expensive and we push migration into the hands of illicit actors," Libal told The AP in a phone interview. "Everyone's thoughts today should be not in politicising it but in making sure that everyone who survived this ordeal is treated with respect and get the protection they need."A group of immigration lawyers and advocates sued Homeland Security Secretary Kelly and other US officials this month alleging that guards on the US border with Mexico have illegally turned away asylum-seekers.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.Money"These criminal organisations, they're all about making money. They have no regard for human life," Homan said.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.Last December, they found 110 migrants trapped and suffocating inside a truck after it crashed while speeding in the state of Veracruz. Most were from Central America, and 48 were minors. Some were injured in the crash.Last October, also in Veracruz state, four migrants suffocated in a truck carrying 55 people.