Flathead County Sheriff Chuck Curry told E! News Wayne Bengston killed Gregory G. Rodriguez Thursday night at the Whitefish home of the mother of Bengston's wife.
The Missoulian reported Bengston was armed with a .44-caliber revolver and shot Rodriguez multiple times.
Whitefish Police Chief Bill Dial said Bengston, 41, then beat and pistol-whipped his wife before fleeing with the couple's 2-year-old son. Bengston dropped off the boy unharmed at a relative's home before driving to his home in West Glacier where he shot and killed himself, the Missoulian said.
Rodriguez, 43, of Sugar Land, Texas, was married with two children, the Billings Gazette reported.
"The victim was here on business and had stopped to talk to a friend for the evening and have a glass of wine," Whitefish Police Chief Bill Dial told the Gazette. "Mr. Bengston came into the home and shot him immediately. We think that it was just a professional relationship, but perhaps the husband thought it was more than that. But that is just conjecture."
The wife, whose name wasn't released, was treated at a hospital and released.