The deadly two-vehicle accident happened just after 6:30 p.m. along State Highway 48, Fox San Antonio reports.
The Texas Department of Public Safety said in a statement that Cameron County Precinct 1 Deputy Constable Ruben Garcia was parked along the highway, assisting DPS with a crash scene when a white Chevrolet Silverado crashed into the back of Deputy Garcia's patrol car.
Deputy Garcia was rushed to the hospital in critical condition, but later succumbed to his injuries.
DPS investigators told NBC 23 that the driver "admitted to being distracted while looking at his phone and driving." He was also suspected of driving while under the influence.