Gangsters with ties to the Zetas cartel helped smuggle migrants across the Rio Grande before they were found locked in a tractor-trailer in Texas, it is reported.

A survivor from the trailer, who has not been named, said he was part of a group of 28 people who paid $700 each to be sailed across the Rio Grande on a raft.

After being taken across the river the man said his group were loaded into the trailer, which had a broken air conditioner, along with up to 170 others.

The survivor, who spoke to the Houston Chronicle, said the group sat in the trailer without moving from Saturday morning until around 9pm, when they set off for San Antonio.

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A survivor from inside the migrant truck discovered in San Antonio has told of how gangsters with connections to the Zetas helped to smuggle him across the Ro Grande before he was locked inside the trailer

The man said he sat inside with up to 200 others from Saturday morning until 9pm when they started out for San Antonio, and the air began to run out (pictured, a memorial for the victims)

Eight people died en-route to San Antonio, while two others later died in hospital from severe dehydration and heatstroke. 30 are still in hospital, some of whom are in critical condition

Four of the dead are Mexican, while another two are Guatemalan. Another 21 Mexicans are known to have been in the trailer, the Consulate General of Mexico said

It was during that journey that air in the trailer began to run out, and the group started banging on the walls to alert driver James Matthew Bradley Jr.

He has since been arrested after the trailer was opened in a Walmart parking lot with the bodies of eight dead migrants inside.

Around 30 others were taken to hospital with conditions ranging from good to critical, before two others died. Police have warned the death toll could still rise.

Of those known to be on the trailer, 25 are Mexican nationals, according to preliminary data from the Consulate General of Mexico.

Four Mexican immigrants are among the dead, along with two Guatemalans.

Bradley, 60, from Clearwater, Florida, made his first court appearance on Monday and was ordered to remain in detention.

Dan Patrick (pictured), lieutenant governor of Texas, on Sunday blamed the deaths of ten illegal immigrants in San Antonio on sanctuary cities

A federal complaint says Bradley told authorities he was driving the trailer to Brownsville, Texas, and was unaware that it was packed with people until he stopped at a Wal-Mart in San Antonio.

The federal complaint says the immigrants packed into the tractor-trailer discovered outside a Texas Wal-Mart were taking turns breathing through a hole in the trailer and pounding on the walls to get the driver's attention.

The complaint says passengers appeared fine during the first hour of their journey, but people later began to struggle to breathe. They were trying to get the driver's attention, but to no avail.

Bradley, however, told cops that he was taking the tractor-trailer to its new owner in Brownsville, and had no idea what was in the cargo hold. He said that it wasn't until he made a stop at the Wal-Mart to urinate that he heard the people pounding on the inside to get out.

'Bradley said he went to open the doors and was surprised when he was run over by "Spanish" people and knocked to the ground,' the affidavit says.

Bradley told police that he noticed 'bodies just lying on the floor like meat' and that he knew at least one of them was dead. He also said that he knew the trailer's refrigeration system didn't work and that the four vent holes were likely clogged.

WHO ARE LOS ZETAS? The Zetas gang, also known as Los Zetas, was originally part of the Gulf cartel, one of Mexico's largest and deadliest criminal organizations which was established in the mid 1980s. Zetas was formed in 1997 by a group of Special Forces defectors which served the larger cartel and acted as enforcers for them. They were hired, predominantly, as bodyguards and assassins and there were 31 of them in total to begin with. Their name translates to 'The Zs' and is derived from the code names given to their leaders - all of which start with the letter Z. Because of its members advanced military training, they brought a new level of sophistication to the underworld and created fresh challenges for US law enforcement agencies trying to crack down on the Mexico's drug gangs. In 2002, they struck out on their own. Unlike other gangs which navigated large parts of the underworld through making deals with violence a collateral side effect, the Zetas MO is torture and terror. They are responsible for the 2010 massacre of 72 illegal migrants whose bodies were found dumped in a mass grave in San Fernando. Images of the victims, who were from other Central and South American countries, shocked the world and illustrated the brutality of the Mexican cartel world. They were savagely killed after refusing to work for Los Zetas or give them money to be released. Advertisement

James Mathew Bradley Jr., 60, of Clearwater, Florida, arrived in San Antonio, Texas court on Monday in handcuffs

During his court appearance, he didn't speak as he was charged with transporting immigrants to the U.S. illegally, resulting in the deaths of 10

Bradley told authorities he was driving the trailer to Brownsville and was unaware that it was packed with people until he stopped at a Wal-Mart

'Bradley stated he went back to the tractor and called his wife but she didn't answer. Bradley said he did not call 911,' the affidavit says.

It was a Wal-Mart employee who called to alert 911 about the suspicious vehicle, around 12:30am on Sunday.

When officers arrived on the scene, they found Bradley in the camper, between the cab and the trailer.

It was not immediately known whether Bradley had an attorney who could speak on his behalf.

Meanwhile, the lieutenant governor of Texas has blamed the deaths of ten illegal immigrants on sanctuary cities.

In a Facebook post on Sunday, Dan Patrick said if it wasn't for sanctuary cities, which refuse to work with the federal government in deporting illegal immigrants, the tragedy in San Antonio would never have happened.

'Sanctuary cities entice people to believe they can come to America and Texas and live outside the law. Sanctuary cities also enable human smugglers and cartels.

'Today, these people paid a terrible price and demonstrate why we need a secure border and legal immigration reform so we can control who enters our country.

'We continue to pray for the families and friends of the victims,' Patrick, a Republican, wrote.

Above, Dan Patrick's Facebook post on Sunday about the tragedy

The ten people were all illegal immigrants. The air conditioning was not working in the back of the truck on a day when the temperatures remained in the 90s

The group were found in the back of the truck, which was parked at a San Antonio Walmart

This is just 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.

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.

San Antonio is about a 150-mile drive from the Mexican border. The temperature in San Antonio reached 101 degrees on Saturday and didn't dip below 90 degrees until after 10pm.

Eldia Contreras wipes away a tear as she takes part in a vigil at San Fernando Cathedral for victims who died as a result of being transported in a tractor-trailer Sunday, July 23, 2017, in San Antonio

The tragedy came to light after a person from the truck approached a Walmart employee and asked for water late Saturday night or early 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.

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 legal.'

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.