Police in the central province of Khanh Hoa on Tuesday launched an investigation and searched the residence and offices of Tran Vu Hai, 57, head of Tran Vu Hai Attorney Office, and his wife Ngo Tuyet Phuong, director of Hanoi Law Co., Ltd.

The couple allegedly evaded tax on properties. They are now under house arrest in Hanoi and prohibited from traveling abroad.

Officers seized documents from Hai’s office, but he refused to make any comments when asked by reporters.

Ngo Anh Tuan, a lawyer  representing the couple, said investigators believe Hai had signed a contract related to his sale of a piece of housing land in Khanh Hoa's Nha Trang in 2016 that allowed the seller to evade VND276 million ($11,800) worth of tax.

Other lawyers said though Hai has not violated any rules related to his profession, his lawyer status would be reviewed if he is found guilty.

Hai has been practicing in Hanoi for a long time and recently expanded to the south.

In 2012 he and a team of lawyers defended Doan Van Vuong, who had opposed local authorities who were expropriating lands in Tien Lang District in the northern city of Hai Phong. Vuong and others’ families won the case, the authorities had to return the lands and top district officials lost their jobs.

In a similar case in 2017, Hai defended people living in Dong Tam, a village on Hanoi's outskirts, who fought for what they believed were their agricultural lands while officials said the lands belonged to the military. In April this year the lands were declared military property and local authorities were told to clearly apprise the villagers.

Hai also defended Huynh Van Nen, who was wrongfully convicted of murder in 1999 and spent nearly 17 years in prison before being acquitted in 2015.