Bui Tin, second from right, with an unidentified United States Air Force sergeant, as American troops evacuated Saigon in 1973. Credit Bettmann Archive/Getty Images.

This post originally appeared at the nytimes.com.

By Mike Ives

Bui Tin, a North Vietnamese colonel who had a prominent role in the Vietnam War’s final moments but later fled the country and became an unlikely critic of its ruling Communist Party, died on Saturday in France. He was 90.

His death, in the Parisian suburb Montreuil, went unacknowledged by Vietnam’s state-run news media but was confirmed on Monday by his longtime friend Nguyen Van Huy, a fellow Vietnamese dissident who lives in France.

Mr. Huy said in a telephone interview that the exact cause of death was unknown but that Colonel Tin had been in a coma and had received kidney dialysis.

Colonel Tin personally accepted the surrender of South Vietnam in 1975. He was also present at the battle of Dien Bien Phu in 1954, when Vietnamese revolutionaries defeated French troops to secure their country’s independence.

Though Colonel Tin was a high-ranking army officer and a onetime disciple of Ho Chi Minh, the country’s founding president, he went into exile in France in 1990. For years afterward he urged his former party comrades to embrace democracy and abandon what he saw as their moribund economic and political ideology.

“His exile embodies the tragedy of Vietnam, and Vietnamese intellectuals in particular,” said Tuong Vu, the author of “Vietnam’s Communist Revolution: The Power and Limits of Ideology,” “as they found themselves in the stranglehold of a corrupt and violent regime that at one point appeared to represent their aspirations.”

When Colonel Tin awoke on April 30, 1975, he probably did not expect to play a direct role in a pivotal moment in Vietnamese history.

Later that morning, he rode aboard a North Vietnamese tank to the presidential palace in Saigon. There, he walked inside to find Gen. Duong Van Minh, the last president of South Vietnam, sitting in a conference room.

Colonel Tin was not a commander but the deputy editor of an army newspaper, Quan Doi Nhan Dan. Because he was the highest-ranking North Vietnamese officer in the room, however, it made sense for him to formally represent the winning side.

“I have been waiting since early this morning to transfer power to you,” General Minh told Colonel Tin, according to a description of the scene in the 2002 book “Our Vietnam: The War 1954-1975,” by A. J. Langguth.

“There is no question of your transferring power,” was the colonel’s tart reply. “Your power has crumbled. You cannot give up what you do not have.”

Colonel Tin then reassured General Minh that he had nothing to fear; it was only the Americans who had been beaten, he said.

“If you are a patriot, consider this a moment of joy,” he said, before making small talk about the general’s tennis game and orchid collection. “The war for our country is over,” he added.

April 30 is now celebrated as Reunification Day in Vietnam. The day commemorates the end of the war as well as the change of Saigon’s name to Ho Chi Minh City.

Many South Vietnamese officials would be imprisoned for years after the war in what the Communist Party called “re-education camps.” Nevertheless, debates within the party would rage for decades over the role that Marxist-Leninist dogma should play in the country’s postwar development.

During a trip to France in 1990 — just as Vietnam’s main patron, the Soviet Union, was crumbling — Colonel Tin declared himself a political dissident and complained that his country was troubled by “bureaucracy, irresponsibility, egoism, corruption and fraud.”

But Mr. Vu, the historian, said that if Colonel Tin had hoped his defection would bring broad political change in Vietnam, he miscalculated.

“He underestimated the resilience of Vietnamese Communism and the regime’s tight control over its officials through a combination of fear and rewards for compliance,” Mr. Vu said.

Bui Tin was born on Dec. 29, 1927, in Nam Dinh, a northern Vietnamese city about 50 miles south of Hanoi.

Colonel Tin, whose father had been a mandarin in Vietnam’s last royal court, became one of a small number of educated Vietnamese who rallied to Ho Chi Minh’s revolutionary cause, Mr. Vu said.

Many of those intellectuals later turned against the Communist Party, which dragged a unified Vietnam through disastrous postwar experiments in collectivized agriculture.

Colonel Tin saw the Soviet bloc’s disintegration as the right moment for his own political about-face. The Communist Party’s leadership “failed to bring liberty and prosperity to Vietnam,” he wrote in The Washington Post in October 1991.

“Rather than improve the abysmal condition of the population, they have blindly pursued sectarian policies designed to maintain their power,” he added.

Even before his defection, Colonel Tin was known as something of a maverick. Notably, he discovered and published Ho Chi Minh’s last will and testament, proving that Ho had wanted his ashes scattered around Vietnam. The discovery exposed what Colonel Tin said was the fraud behind the party’s decision to build a mausoleum in Hanoi for the country’s founder.

Colonel Tin might someday have become chief of the Communist Party “if he had only thought about himself,” said Vo Van Tao, a Vietnamese political activist in the southern city of Nha Trang. “But he was an independent thinker with a democratic outlook who disagreed strongly with the regime.”

Mr. Huy, the colonel’s friend, said that Colonel Tin is survived by his wife, Le Thi Kim Chung; a daughter, Bui Bach Lien; a son, Bui Xuan Vinh; four siblings; and five grandchildren.

Today, Vietnam is a haven for foreign investors seeking a place with cheap labor and a relatively stable political environment. And despite steady waves of online dissent from the Vietnamese public, the party has maintained its grip on power.

It apparently never forgave Colonel Tin, who forged a friendly relationship with the United States soon after going into exile.

In 1991, Colonel Tin traveled to Washington and testified before a Senate committee that dealt with American prisoners of war. He also met with Senator John McCain of Arizona, a former prisoner of war in Hanoi, to discuss what the senator later described as their “mutual interest in promoting democracy in Vietnam.”

After Colonel Tin spoke to the committee, Mr. McCain approached him and stretched out his palm for a handshake. He got a hug instead.