The Department of Special Investigation (DSI) has accepted the disappearance of Karen rights activist Porlajee "Billy" Rakchongcharoen as a special case for investigation.
This was approved in the Thursday meeting of the Board of Special Cases, chaired by Deputy Prime Minister and Justice Minister Prajin Juntong.
Mr Porlajee, who fought against eviction orders and had been in conflict with government officials at Kaeng Krachan National Park in Phetchaburi, was last seen on April 17, 2014, in the custody of state officials. At the time of his arrest, Mr Porlajee was helping his relatives, a group of ethnic Karen, to sue Chaiwat Limlikit-aksorn, the former chief of Kaeng Krachan National Park, for setting fire to their bamboo huts and rice barns in a series of forest evictions.
Mr Chaiwat confessed to arresting the activist for collecting wild honey, but claimed that he released him after a warning. The claims were disputed by Mr Porlajee's family who later filed a series of complaints with the authorities. Mr Porlajee has never returned home.
Mr Chaiwat and his team faced a murder charge related to Mr Porlajee's disappearance but were eventually acquitted for lack of evidence and were reinstated into state service.
Last year, the DSI turned down the request by Mr Porlajee's wife, Pinnapa "Mueno" Prueksapan, for the agency to treat her husband's disappearance as a special case.
Ms Pinnapa later petitioned the National Human Rights Commission to seek assistance and appealed to the DSI to accept the case.
A DSI source said the board's decision came from complaints by international organisations that Thai authorities lacked efforts to deal with the enforced disappearance cases.
Referring to Mr Porlajee's case, the source said investigators searched a vehicle used by Kaeng Krachan National Park officials following the activist's disappearance but it was found to be cleaned before the inspection.
About 200 villagers and witnesses have been questioned about the case, but no one gave useful statements, the source said, adding the park officials who were on duty when Mr Porlajee went missing have been interviewed but they all denied any involvement.
The board also resolved to accept as a special case the encroachment of Hat Chao Mai National Park in the southern province of Trang, according to the source.
No information was available when the alleged offence took place or who was involved.
Meanwhile, another three cases raised by the DSI were shot down by the board.
The first concerns offenders who falsified identification cards and impersonated others by using their IDs. The second is associated with the unrest in the insurgency-plagued far South.
Another involves suspected money laundering in connection with state advertising revenue embezzlement by Rai Som Co, owned by former TV news anchor Sorrayuth Suthassanachinda.