A Montana camper whose mutilated body was found in a forest last month was brutally killed by a stranger he welcomed to his campsite and offered a beer, the authorities said this week, a gesture they say ultimately led to the killer’s arrest.

The stranger, Daren Christopher Abbey, 41, of Basin, Mont., who was working in construction in the Big Sky area of southern Montana, was arrested on Saturday after the authorities linked his DNA to that found on a beer can on the floor of a tent belonging to the victim, Dustin Kjersem, 35, according to court records.

Mr. Abbey confessed on Tuesday to killing Mr. Kjersem, 35, and was later charged with deliberate homicide, Dan Springer, the sheriff of Gallatin County said at a news conference on Thursday.

Mr. Abbey encountered Mr. Kjersem by chance, the authorities said, noting that they still didn’t know the motive for the killing and that the investigation could continue for months.

“This appears to be a heinous crime committed by an individual who had no regard for the life of Dustin Kjersem,” Sheriff Springer said.

On Oct. 10, Mr. Kjersem traveled to a forested area near Big Sky to camp, the authorities said. He had planned to pick up his girlfriend the next day, a Friday, so the two could spend the weekend camping.

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