IDAHO FALLS - A husband murders his wife's boyfriend in the Walmart parking lot off Utah Avenue after learning of a love affair.

Keith Matthias was a math teacher at Idaho Falls High School.

"Dispatch received a call from Jennifer Matthias, that her husband had just killed someone in the parking lot," says Sgt. Phil Grimes, with the Idaho Falls Police Department.

Around 7pm Friday night, Jennifer was having dinner with her husband. She told him about an ongoing affair with Jack Purcell. After she left the restaurant, her husband followed her. She called her boyfriend for help, and parked at the Idaho Falls Walmart.

Within minutes, her boyfriend arrived and had a heated argument with her husband. But then, her husband got out of his car, and shot her boyfriend multiple times in the head with a revolver handgun. The husband then got back into his car, circled the truck, got out again, and fired one last bullet into Purcell's skull.

The husband then drove away, but was followed by witnesses who gave police his location.

"He refused to stop. So officers performed a pit maneuver," says Grimes.

Once stopped near Hawthorne Elementary, Matthias didn't take long to make his final decision.

"The car stops. Keith gets out of the vehicle with the handgun down to his side. One officer fires a tazer which has no affect. Keith is pacing around, puts the gun to his head, and fires, that's all within about 20 seconds," says Grimes.

Why did officers only use a tazer gun?

"Basically, there is no threat towards the officers until he points the gun. If he had moved the weapon towards the officers, he most likely would have fired at that point," adds Grimes.

Did the wife do the right thing in driving to the Walmart parking lot?

"We do tell people and victims, if they're afraid that if someone is following them, I think she did. But probably the only other thing she could have done was contact the police or come to the police department," Grimes explains.

Matthias does not have a previous criminal record in Idaho.

This is the second murder in Idaho Falls in 2009, the first was a stabbing in June. (less info)