A Dallas man has been arrested on a charge of smuggling migrants after more than three dozen people were found in and around a big rig that was stopped in San Antonio, federal prosecutors said Friday.

Aron Bernard Griffin, 49, was arrested Thursday night at a gas station after local police received reports from resident who said they saw people in the back of the tractor-trailer he was driving, prosecutors said in a statement. Police initially reported finding 29 at the scene and federal immigration agents ultimately detained 41 migrants who were in the U.S. without legal permission, according to prosecutors.

Griffin was being held in San Antonio ahead of an initial court appearance Friday, prosecutors said. It was not immediately clear if he had a lawyer who could speak for him.

Prosecutors said Griffin told federal agents that he had made an agreement with another person to pick up the migrants in Laredo and transport them to San Antonio for money.

One of the migrants was taken to a hospital for dehydration, San Antonio Fire Department spokesperson Joe Arrington said Thursday. A Homeland Security Investigations spokeswoman did not immediately respond to questions about the health and age of the migrants Friday.

The smuggling of migrants in trucks is a common practice and can become deadly in the intense heat of Texas summers.

In July 2017, authorities said they found more than three dozen people, including nine who were dead, in a truck’s trailer after an employee at the San Antonio Walmart where it was parked overnight called the police.