(CNN) -- A pro-democracy activist released from a Vietnamese prison was on his way to his California home after nine months in detention, according to his family.
Nguyen Quoc Quan, who holds a U.S. passport, was arrested April 17, 2012, at Ho Chi Min City's Tan Son Nhat International Airport. He was originally charged with terrorism and attempting to overthrow the government, but those charges were later reduced to subversion.
His deportation Wednesday was a surprise, following the postponement of his trial last week.
State media said that Nguyen, 58, of Elk Grove, California, admitted to taking part in illegal activities and was flown out Vietnam for humanitarian reasons.
But the activist's wife said that when he called her before leaving Vietnam, Nguyen denied ever admitting to wrongdoing and said that he was not finished working for democracy there.
Nguyen's family and U.S.-based legal counsel welcomed the news.
"Dr. Quan's release comes as a major and wonderful surprise, given that the government has on trial 22 people right now for subversion, and recently convicted 14 others of similar charges based on protected advocacy of nonviolent democratic reform," said Linda Malone, a professor at William & Mary Law School in Virginia.
"There is no question that the media attention, public outrage and efforts of the State Department were critical in preventing conviction of a U.S. citizen for exercising a clearly protected human right to freedom of speech and thought," she said in a statement.
Nguyen's wife, Ngo Mai Huong, said Nguyen had gone to Vietnam planning to visit his younger sister and talk about democracy and the rule of law.
Ngo told CNN that she got a phone call early Wednesday from a U.S. consular official, who told her that she "had better sit down" before he delivered some news.
"I thought that it had to do with his health or that something had gone wrong at the trial," she said from California. "Instead, he said my husband was on a plane headed home and I couldn't speak. I just cried and cried."
Nguyen was "an important member of leadership" in the Viet Tan democracy organization, says the group's spokesperson, Duy Hoang.
The former high school teacher went to Vietnam in April to meet with other grassroots democracy activists, but was arrested at the airport on arrival, Duy said.
According to a report published last year in the Communist Youth Union-run Tuoi Tre news, "police caught (Nguyen) bringing documents on terrorist training to allegedly incite demonstrations in Ho Chi Minh City as well as other provinces and cities" during festivities marking the reunification of North and South Vietnam and May Day.
Vietnam's Security Ministry determined that Nguyen planned to hold a "demonstration and terrorist activities planned by ... Viet Tan," said a report in the state-run Vietnam News Agency.
"The government detained him because he was opposed to them," said Duy. "But when they couldn't substantiate the terrorism charges against him first they dropped them to subversion and then ultimately they just released him because the publicity and political pressure from the U.S. and politicians in Washington was too strong."
The Viet Tan group -- which has offices in California, Japan, Australia and France -- says on its website it is "committed to peaceful, nonviolent struggle" to defend human rights and promote democracy despite what it calls a "backward dictatorship."
This was not the first time Quan had been detained in Vietnam.
He was released in 2008 after serving six months in prison for a terrorism conviction, according to Tuoi Tre news. Viet Tan said in that case he'd actually been detained in November 2007 "for distributing materials promoting nonviolent tactics for civil resistance."
But Nguyen appears ready to keep up his pressure for reforms.
"My husband said that even after months in prison he was better off and freer than the Vietnamese people today," said Ngo. "He said that to do something good you have to be ready to pay a price."