Nguyen Minh Son, 60, a Facebook user who often speaks out about Vietnam's political and social issues, has been detained by the Security Investigation Agency of the Hanoi Police Department, which also searched his house.

Tran Bao Han, Son's nephew, confirmed the news with RFA, adding that after Thursday’s search, police only gave the family a single document titled "Notice about the application of detention measures.”

According to the notice, Son was questioned and will be detained from Sept. 28, 2022 to Jan. 25, 2023. The family is still unclear under what offenses Son is being held.

“In the morning, the police agency invited my uncle to a local police station for interrogation and arrested him there, then brought him back to search his house. Now he is held in Hoa Lo,” a temporary detention center managed by the city Police Department, Han said.

Some of his documents, books and computers were taken away. The problem is that we still don't know what [allegations have been made] against him. They have just detained him for investigation.”

On the morning of September 28, Mr. Son went to the headquarters of the Security Investigation Agency of the Hanoi Police Department for interrogation after a summons from the agency.

"My uncle was summoned… once before, but this time, I suspected that they would arrest him," Han said.

The summons letters require him to “work” with an investigator named Nguyen Huu Dung, about a video clip that Son posted on his Facebook page, named "Son Nguyen," on December 31, 2021. This video had been removed from his page.

RFA contacted investigative officer Nguyen Huu Dung. When asked about what the accusation was, Dung said he couldn't hear clearly and hung up. The RFA reporter called back, but he didn't answer the phone.

Nguyen Vu Binh, a friend of Son, said Son often participated in peaceful protests and also expressed his views on the social situation in Vietnam on his personal Facebook page

“As far as I know, he participated in many peaceful demonstrations in 2017 and 2018,” Binh said. “He met other activists who criticize the government as well as sharing his views on Facebook but there haven't been any protests in a while, so I was a bit surprised when he was arrested."