Michael Phuong Minh Nguyen, 55, pleaded guilty to the charges on Monday and was sentenced to 12 years in prison. His lawyer said he had asked for a reduced sentence in order to be reunited with his family.
Mr Nguyen’s family denied charges against him and alleged that Mr Nguyen was visiting elderly relatives in Da Nang when he was detained.
Mr Nguyen was born in Vietnam, but has lived in the US since he was a child and has American citizenship. His wife and children live in Orange County, California.
According to official charges, while living in the US, Mr Nguyen became engaged with controversial social issues in Vietnam such as protests against pollution by the company Farmosa and Chinese aggression in the South China Sea. In August 2017, through these connections, Mr Nguyen arrived in Vietnam and was introduced to a secret group, SAU, whose goal was to remove the Vietnam Communist Party from power through popular protests, armed struggle, and occupation of government buildings in Hanoi and Ho Chi Minh City. According to the indictment, Mr Nguyen became a member of SAU and contributed $2,000 to its operations, including to acquire weapons.
In July 2018, the group was apprehended in Ho Chi Minh City. Two other members of SAU were arrested along with Mr Nguyen. Another was charged with aiding and abetting.
Mr Nguyen has been detained by the Vietnamese authorities for 11 months. His wife, Helen Nguyen, said he has been able to talk to the US Embassy in Hanoi once a month, and appears to be in good health.
Mr Nguyen’s family is concerned that he has not received due process and adequate legal representation, according to his brother-in-law Mark Roberts. Activists have been calling for his release; a petition on Change.org has received nearly 95,000 signatures as of June 24, 2019. His wife Helen attended President Trump’s State of the Union address in January as a guest of Representative Katie Porter to call attention to his plight.
The US State Department has not indicated whether it would intervene diplomatically on Mr Nguyen’s behalf. A spokesperson declined a request for comments from NBC News, citing privacy concerns.