Mr. Page had shared some of those journeys into darkness, and his visit to Pkhar Doung was the latest of many searches in what he called “a 25-year madness” in pursuit of the bones of the man he calls his brother.

Weeks earlier two bounty hunters made a false claim to have found them, reviving interest in the disappearance and spurring American investigators to step up the search for the missing journalists.

Mr. Page said, “I don’t like the idea of his spirit out there tormented,” a wandering ghost that could find rest, as many in Asia believe, only after proper funeral rites. “There’s something spooky about being M.I.A.”

Mr. Page is also seeking a measure of peace for his own soul, scarred like his body from the traumas of combat, from nearly fatal wounds and from the loss of friends, trying to put together what he calls “an enormous jigsaw puzzle, bits of sky, bits of earth.”

“I don’t think anybody who goes through anything like war ever comes out intact,” he said. “I suppose the closure of Sean’s fate also has to do with closure of the whole war experience.”

Theirs was an intimacy forged by shared danger and by what Mr. Page calls the magnetic pull of two only sons searching for a bond.

Image Dana Stone and Sean Flynn, riding motorcycles into Communist-held territory in Cambodia on April 6, 1970 Credit... Terry Khoo, courtesy of Perry Deane Young

“We could have been brothers, and felt as though we were,” Mr. Page wrote in a memoir, “Derailed in Uncle Ho’s Victory Garden.” “We would sit for hours in the same room, hardly speaking yet in total communication, a vibration as intimate as between lovers.”