William Nardin and his wife were driving across the Texas panhandle Monday afternoon, headed for a Thanksgiving gathering in Las Vegas, when a pickup truck sideswiped their rental car, police say

The pickup didn't stop, so the Nardins called 911 and tailed the truck westbound on Interstate 40, which cuts across the panhandle from Oklahoma to New Mexico. When the other driver exited the highway 30 miles later near the town of Groom, Nardin followed, pulling into a gas station after the truck.

An argument erupted. The other driver pulled out a handgun, shooting Nardin at least one time in the chest, said Tam Terry, the sheriff of Carson County, Texas. Nardin, 65, of the 9800 block of Southgate Lane in St. Louis County, died at the scene. His wife, Marilyn, was not injured.

The driver of the pickup — William G. Franklin, 81, of Wellsville, Kan. — was arrested and held Monday night at the Carson County jail on suspicion of murder, the sheriff said. Franklin is claiming self-defense.

The sheriff said Nardin either tapped on the window of Franklin's truck or perhaps broke the glass during the argument.

Sheriff Terry said the damage to the Nardins' Chevrolet Impala rental car from the highway collision was minor, a bit of rubber smudged off onto the left rear fender. It was possible, the sheriff said, Franklin did not know he had hit the other car.

"No matter how you look at it," Terry said, "it's a tragedy that someone lost their life over a fender-bender."

Marilyn Nardin was taken to a hotel in Amarillo, about 40 miles west of the shooting scene. She has family in the Dallas area, who are headed to meet her. Terry said she was "obviously shocked."

Franklin, who was headed to a holiday gathering in New Mexico, will be arraigned in court this morning.

"One person is saying this is road rage and the other is saying it's self defense," Terry said. The sheriff said that that would be up for the court to decide and that he was glad he didn't have to make those decisions.

William and Marilyn Nardin are listed in state records as operators of Command Operations Center, based at their home near Sunset Hills.

Nardin's neighbor, Wayne Robinson, 73, said the Nardins lived in the same house for more than three decades. Nardin was a retired U.S. Marine and designed models used in military training, Robinson said. He said Nardin's wife, Marilyn, is a nurse.

Robinson said Nardin frequently traveled for work and often hosted a wargaming gathering at his house.

In the early 1980s, Nardin, while working as a sales representative for Jaguar cars, insisted Robinson's son, Douglas, drive to his high school prom in a shiny, new black Jaguar.

"They had quite an evening," Robinson said of his son's prom night with his friends.

In a story that ran in the Post-Dispatch in 2002 about a drill William Nardin was running at Lambert-St. Louis International Airport, Nardin said the company put together high-pressure scenarios for businesses and the armed forces. Its aim was described as to "get people used to dealing with stress and thinking on their feet."

In another story that ran in 2003, William Nardin was identified as a Marine who was discharged in 1967 as a corporal.

Several truck drivers witnessed the shooting, which happened at 3:10 p.m. Monday, but left the scene. The sheriff's department is trying to track them down in an effort to put together a more complete picture of how the dispute and shooting unfolded.

Terry said his department had handled at least one road rage case previously, when a trucker stabbed another in a fight a few years ago.

"But," sheriff Terry said, "never like this."

-Joel Currier of the Post-Dispatch contributed to this report.