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A former Utah state trooper suspected in a series of fatal rush-hour shootings near Dallas had an addiction to painkillers and a warrant had been issued for his arrest in connection with a recent robbery, according to Texas and Utah authorities.

Dallas police said Tuesday they think 37-year-old ex-trooper Brian Smith was responsible for at least one death that resulted from the shootings. They declined to comment on another death in neighboring Garland because it was outside their jurisdiction.

Garland police spokesman Joe Harn said his department has not been able to make a definitive connection between Smith and the killing there, but acknowledged that he fit the description of the highway shooter: a balding, 40ish white man.

"We certainly hope it is him," Harn said. "But we are going to have to see more concrete evidence."

Smith was in critical condition on life support Wednesday morning at a Dallas hospital from a self-inflicted gunshot wound. Police said he shot himself in the head early Tuesday morning after a brief standoff and more than six hours after the roadway shooting spree ended.

Dallas police Lt. Craig Miller said they linked Smith to the killing in Dallas because the bullets from the standoff were a match. The weapon was a high-caliber semiautomatic handgun, Miller said.

"We feel safe in saying (Smith)... was the shooter," Miller said.

Before the standoff, two people were fatally shot and a third was injured in four rush-hour shootings Monday along or near a Dallas-area highway. Police said the victims appeared to have been selected at random.

The crime spree appears to have begun in Garland, where a man police identified as Smith jumped over a pharmacy counter at a grocery store and stole Oxycontin pills.

Minutes later, the first shooting happened in Garland when a driver pulled up alongside a small Nissan stopped at a red light and began shooting, Harn said. The Nissan's driver, 20-year-old Jorge "George" Lopez of Rowlett, was killed.

Witnesses told police the driver headed toward Interstate 635 in Dallas, where shots were fired at an 18-wheeler a short time later. The driver of the 18-wheeler, identified by police as Kenneth Black Harly, was not hurt.

Minutes later on the same highway, a gunman shot and killed 42-year-old William Scott Miller, the driver of a United Van Lines rig, Miller said.

Police said the driver, a military veteran who was about to fly home to his wife and two young daughters in Frankfort, Ky., for the holidays, was able to bring his truck safely to a stop before he died.

"The act he did in and of itself I consider to be heroic," Miller said. "Despite being mortally wounded, he was able to control his rig to the point where other drivers weren't injured."

After the shooting of Miller, another semitrailer was fired upon a half-mile away on the same interstate. The driver, 46-year-old Gary Roberts, was injured by debris and glass but not struck by any bullets. His right eye was hit by shattered glass and he needed several stitches in his fingers, said Bedford Wilhite, who works with Roberts at Dugan Truck Line.

Roberts told Wilhite he is "much blessed and thankful to be alive."

"It's just absolutely stunning to me that something like this would happen," Wilhite said. "This is our way of surviving in this country — truckers hauling goods up and down the highways. Why would someone want to take potshots like this at our drivers?"

A spokesman with the Utah Department of Public Safety said Smith had been a trooper since 1996 but resigned in May because of "personal issues." Smith, who was a sergeant in the Utah Highway Patrol, had his peace officer certification revoked following a January incident.

According to a report by the Utah Peace Officer Standards and Training investigations bureau, Smith drank two pints of hard liquor and drove his patrol car home. When he arrived, he summoned his clergyman, who sat with him in the patrol car. Smith held a gun to his own head and threatened to kill himself. The clergyman eventually grabbed the gun when Smith placed it on the dashboard. Smith later confirmed the details of the incident to an internal investigator.

Smith was taken to a hospital for treatment and a psychological evaluation, according to the report, The Dallas Morning News reported Tuesday in its online edition.

"Smith also admitted, in the past, he had stolen and used Demerol and one Ambien tablet from his father-in-law's dental office," the report says. "Smith's abuse of alcohol and prescription medications started after an on-duty traffic accident."

A Utah Department of Public Safety investigation found that Smith drove under the influence, committed theft and was engaged in conduct that would "tend to disrupt, diminish or otherwise jeopardize public trust and fidelity in law enforcement."

"Up to that point, he was an amazing person. Very motivated, very career-oriented," said Sgt. Jeff Nigbur of the Utah Highway Patrol, who described Smith as a good friend. "He served this state very well."

Smith resigned after 12 years and moved to Keller with his family, said Nigbur.

Southlake authorities obtained a warrant for Smith's arrest in connection with a Dec. 17 robbery of a woman in a suburban shopping center parking lot. The woman was sitting in a vehicle when a man approached and shot a liquid in her eyes, temporarily blinding her.

"He had some type of squirt gun," said Southlake police spokesman Mike Bedrich. When she covered her face, the suspect took her purse.

Detectives later identified Smith on surveillance footage using the woman's credit cards.

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