He said a Border Patrol agent initiated the pursuit before a unit for the sheriff's office took over.
Authorities are investigating the scene where a vehicle full of undocumented immigrants being chased by Border Patrol agents crashed.
Five immigrants are dead and several others were injured when a police chase ended in a crash Sunday in Big Wells southwest of San Antonio, according to KSAT News. The driver was not seriously injured and taken into Homeland Security custody, Dimmit County Sheriff Marion Boyd told reporters.
Boyd said the vehicle was going more than 100 miles per hour before the crash.
"We've seen this many, many times, in not only this county but other counties along the border", Boyd told CNN. "This is I think a flawless example of why our borders need to be secured".
Television images showed the smashed vehicle missing at least two wheels, with debris strewn across the road at the Big Wells city limit. 12 immigrants were ejected and four died on scene.
Fourteen people were inside, including the driver and passenger. All of the people killed were immigrants.
During a press conference, Boy said 14 people were in the vehicle, including the driver and passenger. Authorities believe the driver and one passenger are USA citizens. He credited "good police work" for the reason deputies started pursuing the vehicle. Dimmit County is directly north of Webb County and east of Maverick County, which border Mexico.