YOUNTVILLE, Calif. — The Pathway Home, a California program that treats troubled war veterans, is part of a large 19th-century veterans complex ringed by the famed vineyards of Napa Valley. Its mission-style buildings and mature stands of redwoods are worlds apart from the Middle Eastern deserts and mountains where many of its residents have fought — and left parts of themselves behind.

On Friday morning, Albert Wong, an Afghanistan war veteran and a former program participant, entered the campus with at least one loaded rifle. Hours later, he and three Pathway staff members whose jobs centered on helping servicemen reintegrate into society were found dead, and Pathway had suffered the very sort of tragedy that it was devised to prevent.

Mr. Wong, who until two weeks ago had been receiving treatment at the home, arrived at a going-away party for two staff members, according to Larry Kamer, a spokesman for the organization.

Mr. Wong ordered veterans out of the room and held three employees hostage.

“He was very calm,” said Mr. Kamer, who said his description was based on the observations of his wife, Devereaux Smith, the nonprofit’s director of development and communications, who was in the room. “He didn’t say much.”