Fred Branfman, a writer and activist who first brought attention to secret U.S. bombing of Laos during the Vietnam War. (Family photo)

Fred Branfman, the first person to draw public attention to a previously unknown U.S. bombing campaign inside Laos during the Vietnam War and who later became a leading antiwar activist in Washington, died Sept. 24 at a medical facility in Budapest, where he had lived for several years. He was 72.

The cause was amyotrophic lateral sclerosis, or ALS, said his wife, Zsuzsanna Berkovits Branfman.

Mr. Branfman, who was born in New York, moved to Laos, a landlocked nation bordering Vietnam, as an education adviser in 1967. He was fluent in the Laotian language and began to hear reports from refugees who had been driven from their villages by relentless bombing attacks.

He visited the refu­gee camps himself and learned that thousands of Laotians had been killed. The picturesque Plain of Jars, a region dotted with giant, hollowed-out stone receptacles, had been reduced to ruins.

“I interviewed over 2,000 people,” Mr. Branfman said in “The Most Secret Place on Earth,” a 2008 documentary, “and every single one told the same story.”

Refugees made drawings of the destruction, which depicted U.S. warplanes flying overhead and dropping munitions from the sky. The toll on local residents, animals and vegetation was immense.

Investigations by Mr. Branfman and others revealed that a secret CIA-built air base in Laos was, in effect, the busiest airport in the world. Bombing missions were carried out over Vietnam, but much of the ordnance was dropped on Laos in an effort to disrupt Viet Cong supply routes.

The Ho Chi Minh Trail, used by North Vietnam to supply Viet Cong fighters in South Vietnam, ran through the area, which was also roamed by communist guerrillas known as the Pathet Lao.

To Mr. Branfman, however, nothing could justify the human cost. He first made his discoveries in 1969 and was deported from Laos in 1971 “under pressure from the United States Embassy,” according to a Harper’s magazine article by journalist Christopher Hitchens.

Writing in the New York Times in 1971, after his return to the United States, Mr. Branfman described what Laotian refugees had told him:

“Each, without exception, said that his village had been totally leveled by bombing. Each, without exception, said that he had spent months or even years on end hiding in holes or trenches dug into foothills.

“The refugees say that the bombing began in 1964.”

At a Senate hearing in April 1971, Mr. Branfman said, “There is a good deal of evidence to suggest that the United States has been carrying out the most protracted bombing of civilian targets in history.”

A subsequent Washington Post investigation concluded: “By the admission of American officials closely associated with the war there, Laos has been the most heavily bombed country in the history of aerial warfare.”

It was later determined that the United States dropped more bombs on Laos in the 1960s and 1970s than on Germany and Japan combined during World War II. Mr. Branfman edited a collection of writings and artworks by Laotian refugees, “Voices from the Plain of Jars” (1972), which highlighted the devastation of the air war in Laos.

In Washington, Mr. Branfman founded the Indochina Resource Center, an information service that was allied with the antiwar movement.

“He made no secret,” journalist Les Whitten wrote in The Post in 1974, “of where his heart was: on his left sleeve, armband high.”

In 1972, he organized a star-studded antiwar demonstration at the U.S. Capitol. Those arrested included singer Judy Collins, Dr. Benjamin Spock, leftist scholar Noam Chomsky, painter Larry Rivers, theatrical producer Joseph Papp and writer Garry Wills.

“Fred was brilliant,” said William Goodfellow, executive director of the Center for International Policy, who worked with Mr. Branfman in the 1970s. “He was one of the intellectual lights of the antiwar movement.”

Fredrick Robert Branfman was born March 18, 1942, in New York City. His father was a textile executive.

Mr. Branfman received a bachelor’s degree in political science from the University of Chicago in 1964 and a master’s degree in education from Harvard University in 1965.

He spent time on an Israeli kibbutz as an undergraduate and, from 1965 to 1967, worked as a teacher in Tanzania. He received a draft deferment to teach and advise educators in Laos, beginning in 1967.

In the mid-1970s, Mr. Branfman moved to California, where he became active in the solar energy movement and served as research director for the failed Senate campaign of former Chicago Seven defendant Tom Hayden.

Mr. Branfman was a research director for California Gov. Jerry Brown (D) from 1979 to 1983 and helped coordinate the state’s outreach to the early high-tech pioneers of Silicon Valley.

He returned to Washington in the mid-1980s to work on the presidential campaign of Sen. Gary Hart (D-Colo.), then directed a nonprofit organization called Rebuild America, which promoted U.S. manufacturing and domestic job creation.

In 1990, after the death of his father, Mr. Branfman abruptly changed the direction of his life. He embarked on a prolonged spiritual exploration that led him to study various religious traditions around the world and to become an advocate for “death with dignity.”

He was known for having almost no possessions beyond a laptop computer and a cellphone. He settled in Budapest about five years ago.

His first marriage, to Nguyen Thoa, ended in divorce. Survivors include his wife of 16 years, Zsuzsanna Berkovits Branfman of Budapest; and three brothers.

In recent years, Mr. Branfman was a frequent contributor to Salon.com, Huffington Post and other publications. He returned several times to Laos, where he spoke with survivors of the bombings and walked among the craters that now mark the Plain of Jars.