An Arizona trooper, who just graduated from the academy in May, was shot dead when a suspect stole a police officer's gun during a struggle, authorities said.
"The [Department of Public Safety] family is in mourning," Colonel Frank Milstead of the Arizona Department of Public Safety said at a news conference overnight. "Lives have been shattered and ruined."
The attack unfolded Wednesday night around 10:17 p.m. after authorities received calls about a driver swerving in and out of the lanes of Interstate 10, throwing items at cars, Milstead said.
Several motorists pulled over on the side of the highway to get the man off the road, Milstead said.
Trooper Dalin Dorris was first to arrive and called for backup within one minute of getting to the scene, Milstead said.
A minute later, two more troopers arrived, including rookie Tyler Edenhofer, who was finishing his last days of field training after graduating from the academy on May 4, Milstead said.
A fight broke out, Milstead said, during which two Goodyear, Arizona, police officers arrived and helped try to take the suspect into custody.
The fight lasted for about eight minutes and involved six law enforcement officers, Milstead said.
The suspect shot troopers Edenhofer and Dorris after he got a hold of a third trooper's weapon during the altercation, Milstead said.
It is unclear if the gun became dislodged from the trooper's leather holster or if the suspect felt it and "took control of it," Milstead said, describing the holster as a "non-retention type holster" with merely a snap at the top and no mechanism release that prevents someone from grabbing it.
The trooper whose gun was used in the shooting was in plain clothes -- jeans and a T-shirt, Milstead said.
"He just looked like he was a citizen observer that night," Milstead said.
Both troopers were shot in the shoulder, said Captain Tony Mapp of the Arizona Department of Public Safety. The bullet went straight through Dorris, but the bullet that struck Edenhofer ricocheted inside his body, Mapp said.
Dorris is in "good spirits considering the circumstances," Milstead said.
Edenhofer died from his injuries. The department was planning to assign him to the Yuma area in southwest Arizona, Mapp said.
"He'd been one of my troopers for 52 days," Milstead said.
Edenhofer was engaged, and his fiancee "had her entire future in front of her and her life with Tyler to look forward to, and that is gone," Milstead said.
"We're all in a little bit of a state of shock this morning," Milstead said. "Our thoughts and prayers are with his family."
The suspect was identified as 20-year-old Isaac King, Milstead said. King has a history of mental health issues and was apparently on medication for anxiety and depression, but he has no criminal history, Milstead said.
King's parents have been cooperative in the investigation, Milstead said. As late as 9:30 p.m. that night, his mother believed he was on the trampoline at the family's home in Avondale, he said.
Milstead said the shooting is "evidence of the violent nature of policing in our nation" as well as "evidence that just because somebody is unarmed doesn't mean they won't become armed and harm somebody."
"I'm incredibly proud of the men and women that show up every night to do this job," Milstead added. "That they're brave enough to come out and face the unknown."
Detectives are still conducting interviews and reviewing physical evidence to determine what happened on the interstate, Milstead said. About 70 items from the roadway have been collected, he said. It is unclear what type of items the suspect was throwing at cars.
Edenhofer's death came just hours after a 17-year veteran of the Milwaukee Police Department veteran was shot dead in the line of duty in Wisconsin.
Gunfire was the leading cause of death among the 73 officers killed in the first half of this year, accounting for 42 percent of the deaths, according to the National Law Enforcement Officers Memorial Fund.
ABC News' Rex Sakamoto contributed to this report.