Le Tung Van, who lives in the Mekong Delta's Long An Province, was put under an investigation by the local police on Friday while on bail due to health reasons.
The investigation came following authorities' verification of tip-offs claiming Van had committed incestuous acts.
In 2022, Van made headlines on the news after instructing several people to create YouTube accounts posting videos containing false content that insulted the reputation of various organizations and individuals, including the Vietnam Buddhist Sangha in Long An, and Vietnamese Buddhist monk Thich Nhat Tu.
Authorities said there was enough evidence to prove that Van had had incestuous relationships with his own children, who live with Cao Thi Cuc, an acquaintance of Van, in a house in Duc Hoa District.
Around 10 years prior, Cuc turned her house into a site of illegal worship and brought several Buddhist statues into the building. Van moved in with Cuc in 2015.
In 2022, when Van was put under investigation for abusing democratic freedom, Cuc was raising eight children in her household, with six of them living with their birth mothers, and two others being adopted.
An investigation is ongoing.
Incest is punishable by up to five years in prison in Vietnam.