Robertson, 37, had been the object of a massive, two-day manhunt that began after East Texas state Trooper Scott Burns was killed during a traffic spot Tuesday night in Marion County.

Robertson was spotted Thursday afternoon parked next to a shed in neighboring Cass County -- not far from the feed store owned by the slain trooper's parents.

Authorities had been tracking Robertson through his cell phone calls and a helicopter pilot had spotted Robertson's Dodge Intrepid and called for reinforcements.

In the car was Robertson's girlfriend, Jennifer Petrick, who authorities said had been with Robertson since the shooting.

A member of the task force that was hunting for Robertson said Robertson called 911 and told the operator he would shoot Petrick if the helicopter did not leave. Petrick got out of the car, the task force member said, and Robertson committed suicide.

Authorities said Petrick, who is jailed without bond in Cass County on parole violations, is cooperating with authorities about what happened before and after the trooper was killed. They have not disclosed what she has said about why the trooper was shot as he sat in the seat of his patrol car.

Burns' family released a statement today thanking the public for the outpouring of support for them. They also expressed anger over the murder of the trooper.

"The family has asked me to also convey to you the anger and frustration they feel over the senseless, cold-blooded act that has cost (daughter) Micah Burns her father," Linden Mayor Kenny Hamilton said. "They were relieved yesterday when the combined efforts of law enforcement ended the search for Scott's killer. They were even more relieved that there was no further loss of innocent life."

Mayor Kenny Hamilton described Burns as a quiet and soft-spoken man who loved his family, his job, fishing and deer hunting.