A former police officer suspected in the fatal shooting of a state trooper killed himself in Texas on Thursday as authorities closed in on his location, officials said.

The body of Brandon Wayne Robertson, 37, was found dead of a self-inflicted gunshot wound in a brushy area just outside of Linden in Cass County. The Department of Public Safety said that authorities had been tracking him with the help of calls he made to 911 and calls to a tip line.

Robertson was named in a capital murder warrant in the death of Trooper James Scott Burns, who was killed Tuesday night after pulling over a car near Lake O' The Pines in East Texas.

Burns didn't have a chance to remove his seat belt as he stopped his patrol car, just before getting shot multiple times with a shotgun, authorities said. A passer-by later used the trooper's radio to call for help.

Robertson was an East Texas police officer for seven years at departments in Rusk County, Overton and Kilgore, according to the Texas Commission on Law Enforcement Standards and Education. He left law enforcement in 1999.

Robertson's girlfriend was taken into custody Thursday. DPS said that criminal charges are pending against her.

Robertson was arrested by Department of Public Safety troopers as recently as April 6, when he was charged in Cherokee County with possession of a controlled substance. He posted a $7,500 bond the next day.

DPS trooper and spokeswoman Sylvia Jennings has said she did not know what prompted the pursuit that ended with Burns' death.