"He was able to get him out of the vehicle and the driver was actually walking", Boyd said.
There were 14 people in the vehicle.
Sunday's crash comes amid widespread protests over President Donald Trump's immigration policies that include separating undocumented children from parents caught sneaking them into the country. "This is I think a ideal example of why our borders need to be secured".
He said four people died at the scene, and several were flown by emergency helicopter to a hospital in San Antonio.
Twelve immigrants were ejected when the auto crash.
Authorities are investigating the scene where a auto full of undocumented immigrants being chased by Border Patrol agents crashed.
While travelling at top speed, the driver lost control of the SUV, which rolled, causing the deaths and injuries, the Texas Department of Public Safety was quoted as saying.
The driver and passenger are USA citizens and are likely to face state and federal charges, Boyd said. Authorities believe the driver and one passenger are USA citizens.
Boyd said his officers have dealt with the driver before, adding he was scouting the area earlier to try and pick up immigrants. They are likely to face state and federal charges, Boyd said. "There needs to be sensors". "We've seen this many, many times, in not only this county but other counties along the border". Four of those people died at the scene, officials stated.
At least five people were killed after an SUV carrying illegal immigrants crashed following a high-speed chase near the Texas-Mexico border, the sheriff said.