It had been nearly four decades that a family agonizingly wondered what had happened to their son and brother — an 18-year-old New Milford man who disappeared while hitchhiking out west.

Recently, they learned his fate was something they had refused to consider for all those years.

David Arthur Stack was shot and killed in Wendover, Utah, in June 1976 — the same month he left Colorado to hitchhike to California.

Stack had been listed as a missing person until early August, when DNA evidence confirmed the body found at a Utah water treatment facility in 1976 was, in fact, the 1975 New Milford High School grad.

His seven siblings are now struggling to accept grim reality.

“We always hoped that it was something better than it ended up being,” said Diane Collentine, the youngest Stack sibling, who lives in New Milford.

James Stack, another sibling who still lives in town, said his family had worked closely with police and authorities in Colorado, where his brother was staying before he had taken off hitchhiking.

"We never stopped searching,” he said.

Without clues, the teen’s parents, who have since died, and siblings speculated year after year about his fate. They wondered whether he had moved to another state, traveled to Europe or developed amnesia, among other possibilities.

“I always thought that he went to Alaska,” said James Stack, who said that’s how he wants to remember his brother.

“Dave,” as his family called him, was 6 feet tall with shoulder-length hair. He enjoyed traveling and meeting new people, his New Milford siblings said.

In his NMHS yearbook, the teen said his favorite pastime was partying.

A member of the school’s Discussion Club, David Stack had many friends, enjoyed rock concerts and may have been the most popular among his siblings, family members said.

“Of all the Stacks, he was the big star,” James Stack said.

Collentine and James Stack also described their sibling as charming and charismatic.

“The grass is always greener,” David Arthur Stack wrote as his quote in his school yearbook.

The other siblings now live in Kansas, Nevada, Colorado and Connecticut, including in Southbury and Winsted. A ninth sibling died several years ago.

The Charley Project, a website that profiles missing people, says Stack left Colorado in June 1976 and planned to hitchhike to one of his siblings’ homes in Berkeley or Truckee, Calif.