The driver of the SUV led officials on a chase until the driver lost control and crashed, killing five people and injuring at least 10 others, reports said.
He said four people died at the scene, and several were flown by emergency helicopter to a hospital in San Antonio. Border Patrol agents stopped two of the vehicles and made multiple arrests, but the third vehicle continued, the statement said.
This article be updated as more details become available.
He said his deputies are often involved in chases pursuing people suspected of smuggling undocumented immigrants and drugs.
Boyd said the driver and one passenger of the passengers were the only US citizens in the vehicle.
He said there were 14 people in the vehicle.
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Sunday's crash came almost a week after more than 50 immigrants were found inside a refrigerated tractor-trailer Monday in San Antonio.
Boyd said the vehicle was going more than 100 miles per hour before the crash. He said one passenger was taken into custody. A fifth person died at a San Antonio hospital.
The passenger, also believed to be a USA citizen, is now in custody.
Boy believes the driver was scouting the area to try and pick up immigrants.
The Trump administration has said tougher immigration policies are needed to deter immigrants from entering America illegally. "We've seen this many, many times".
Images from the scene appeared to show a large four-door SUV-style vehicle badly wrecked in the middle of the road. The Agency added that the incident is now being investigated by Homeland Security Investigations, the US Border Patrol, Texas Department of Public Safety, Dimmit County Sheriff's Office, and Customs and Border Protection's Office of Professional Responsibility.