(CNN)  -- The former Utah state trooper suspected in a series of roadway shootings earlier this week died Wednesday, the Dallas County Medical Examiner's Office said.



CNN affiliate KSL in Salt Lake City, Utah, provided this file photo of the Dallas suspect, Brian Smith.



Police said Tuesday that Brian Smith attempted suicide after Monday's shootings. Smith was brought to a local hospital in serious condition, officials said



At 7 p.m. Wednesday Smith died at Parkland Hospital, the medical examiner's office said. An autopsy is slated for Thursday.



Two people were killed in the shootings along a three-mile stretch on and near the LBJ Freeway, about 10 miles northeast of downtown Dallas.



Police used ballistic tests to link Smith, a 12-year veteran of the Utah state police, to three of the four shootings, Dallas Police Lt. Craig Miller said Tuesday.



Miller said Smith was a suspect in both nonfatal shootings and one of the fatal shootings. He said it was unclear if Smith was a suspect in the fatal shooting that occurred first.



The first attack occurred in the city of Garland at about 5:41 p.m. Victim Jorge Lopez, 20, was sitting in his Nissan at a traffic light in Garland when a man in a pickup pulled alongside him and fired shots into his car, killing him, Officer Joe Harn of the Garland police said.



A few minutes later and two miles away on the LBJ Freeway, a gunman fired at two tractor-trailers.



While one driver escaped injuries, William Scott Miller, 42, of Frankfort, Kentucky, was shot to death behind the wheel of a United Van Lines truck, police said.



"He was going to be traveling home," Lt. Miller said. "He was about to park his rig. He was going to get on a plane to fly to be with his wife and children for the Christmas season and then come back to this location."



Miller called the truck driver a hero because he was able to control his rig before he died -- preventing other motorists from being hurt.



The fourth attack came a mile west on LBJ Freeway, where gunfire shattered the windshield of another tractor-trailer. The bullets missed the driver, but flying glass caused minor cuts, police said.



Smith, 37, left his trooper job in Utah after he was caught abusing alcohol and drugs, CNN affiliate WFAA reported, citing an official report. The sergeant began using drugs and alcohol after his patrol car was rear-ended while he was writing a ticket, according to the report by Utah Peace Officers Standards and Training.



He moved to Texas shortly afterward, the station said.



Harn told WFAA that Smith's wife had phoned police Monday to say her husband was suicidal and driving around with a gun. Police were able to locate him using cell phone transmission towers. A three-hour stand-off followed, ending when Smith shot himself in the head, Harn said.
Who were shot and killed? Who was hospitalized in serious condition after a suicide attempt? Who was tied to at least three of four Dallas shootings? Who is the ex-Utah officer?
Two people Brian Smith Brian Smith. Brian Smith.
question: Who were shot and killed?, answer: Two people | question: Who was hospitalized in serious condition after a suicide attempt?, answer: Brian Smith | question: Who was tied to at least three of four Dallas shootings?, answer: Brian Smith. | question: Who is the ex-Utah officer?, answer: Brian Smith.