SAN ANTONIO — Investigators believe a truck driver accused in the deaths of 10 people found inside a packed, sweltering tractor-trailer is just one member of a larger organization involved in human smuggling that they are looking to identify and dismantle, a U.S. immigration official said Tuesday.

Some of the 29 identified survivors have told authorities they hired smugglers who brought them across the U.S. border, loaded some of them onto trucks that took them to the tractor-trailer, and marked them with different colored tape to identify them to various smugglers who would be picking them up after the tractor-trailer reached its destination.

“We’re certainly not stopping at looking at the driver. We’re trying to investigate and identify the different cogs, the stash houses, the other members, where the money came from,” Shane Folden, special agent in charge of U.S. Immigration and Customs Enforcement’s Homeland Security Investigations office in San Antonio, told The Associated Press.

The driver, James Matthew Bradley Jr., 60, of Clearwater, Florida, is facing charges of illegally transporting immigrants for financial gain, resulting in death. Bradley could face the death penalty. Authorities allege he drove a trailer full of immigrants from South Texas that was discovered in the parking lot of a Walmart in San Antonio early Sunday morning.

Folden said charging Bradley 0is just the first step in the case as investigators work to find others involved in the scheme, including those responsible for facilitating money transfers and bringing the immigrants across the border.

“The ultimate goal is to dismantle the complete organization. You don’t get there by only focusing on one aspect. You have to look at potential targets and potential related locations, both north and south,” he said.

U.S. Rep. Henry Cuellar from Texas said he was informed by law enforcement the tractor-trailer had cleared a Border Patrol checkpoint 29 miles north of the border on Interstate 35 near Laredo. Cuellar said he didn’t know whether the immigrants were loaded into the truck before or after it crossed the checkpoint.

U.S. authorities are still trying to determine how many people were inside the tractor-trailer because some fled before police arrived, Folden said.

Thirteen people who rode in the trailer remained hospitalized Tuesday in San Antonio, said ICE spokesman Greg Palmore. He declined to say how many were critical or in life-threatening condition. Officials say at least 29 people survived the smuggling attempt.

Delmin Darío López Colomo, 23, a Guatemalan survivor who remains hospitalized, said the migrants in the tractor-trailer were delivered by various different smugglers, according to Cristy Andrino, the consul of Guatemala in McAllen, Texas.

Adan Lara Vega, 27, a migrant from Mexico who survived the smuggling attempt, told the AP on Monday that they boarded the truck on a Laredo street Saturday night for the two-hour trip to San Antonio. He said the trailer was already full of people, but it was so dark he couldn’t tell how many.