Detectives had been working around the clock to solve the death of Cody Harter, Sgt. Chris Depue, a spokesman for the Lee's Summit Police Department, told ABC News over the weekend.
The suspect, 58-year-old Nicholas Webb, has been charged with second-degree murder, according to a criminal complaint filed Thursday in Jackson County. On Saturday, two hours after Harter was attacked, Webb was arrested in Liberty, Missouri on charges of possession of dangerous drugs and driving under the influence, the complaint states.
On Wednesday, a detective from the Clay County, Missouri Sheriff's Office obtained body camera footage from the arrest, which revealed that Webb had been driving a gray four-door Mitsubishi Lancer, according to the complaint. The arrest report stated that Webb was in possession of a knife in his right pants pocket, the complaint states.
Investigators conducted surveillance of Webb's home later that day, and when he pulled up in the gray sedan, they brought him in as a "person of interest," the complaint states.
During the interview, Webb admitted that the other driver yelled at him, saying, "Hey, this is a merging lane," and that he responded, "all right dude," the document states. Webb said there was no pushing or swinging, and that he only stopped his car when the other driver stopped. He said that the driver didn't seem mad and got back into his vehicle after stating for a second time that it was a merging lane.
Webb stated that he did not kill or hurt Harter.
Officials said in a press conference Thursday that Webb was previously sentenced to 35 years in prison in 1981 for second-degree murder but was released after about 15 years because the "85 percent rule did not exist yet."
Webb faces "extremely serious time" if he is convicted," authorities said.
Several witnesses saw the two men "arguing" outside of Harter's truck and the suspect's vehicle -- both were pulled over and jutting out of a median between Interstate 470 and MO-291, Depue said.
Harter was driving his maroon Chevy Silverado C71 extended cab, with a newly purchased lawnmower in the back, around 7:30 p.m. Saturday when he apparently pulled over and stepped outside to argue with another driver. The suspect was driving a "mid-size car," Depue said.
"Both cars were stopped near the middle of the road," Depue said, noting multiple witnesses would have had to navigate around them to avoid seeing the men square off.
"The witnesses have told us that it looked like they were arguing," he added. "You could tell by their body language there was an altercation."
Moments later, a wounded Harter was then seen staggering into traffic, eventually finding the arms of a good Samaritan who held him and prayed with him until his dying breath, Cody Harter's mother, Kerrie Harter, said.
"At this point, police are looking at road rage as the probable cause," Depue said. "There's nothing to indicate a robbery occurred."
Kerrie Harter described her son as a dutiful soldier who "would help anybody" and was about to graduate with an engineering degree from Missouri Western State University.
"He had been to war and back, and to die because someone was angry?" she said. "My son drove 65 miles per hour because he was so frugal with his gas mileage. I can only imagine someone was upset because he wasn't going fast enough. But that's not a reason to take his life and leave him there."
In a statement, the Missouri National Guard said it was "sad to learn of the death of Senior Airman Cody Michael Harter ... our thoughts and prayers are with [his] family and loved ones."
Cody Harter enlisted in the National Guard in 2012 and completed an overseas deployment to Qatar as part of Operation Enduring Freedom, the statement confirmed. Harter, his family said, recently was part of the military response to hurricanes that ravaged both Houston and Puerto Rico.
ABC News' Ben Stein contributed to this report.