The Department of Special Investigation (DSI) has submitted additional information relating to the disappearance of Karen rights activist Porlajee "Billy" Rakchongcharoen to the Office of the Attorney-General (OAG), which the office needs for further legal action.
DSI director-general Triyarith Temahivong said investigators have questioned seven witnesses about four issues as requested by prosecutors, in addition to questioning more forensic experts and examining all evidence related to the case.
"The DSI will deliver justice to Porlajee's family," said Mr Triyarith.
Surapong Kongchantuk, president of the Cross-Cultural Foundation, said that on Sept 9 last year, the OAG asked the DSI to provide more information.
That included a test to ascertain the matrilineal connection between Porlajee and his mother and the result of a special forensic analysis of the bone fragments believed to be those of the missing activist, Mr Surapong said.
At that time, an OAG panel had said there was not enough evidence to conclude if the bone fragments indeed belonged to Porlajee.
As a consequence, there was insufficient proof to link four suspects -- Chaiwat Limlikit-aksorn, a former head of Kaeng Krachan National Park, Bunthaen Butsarakham, Thanaset Chaemthet, and Kritsanaphong Chitthet -- to Porlajee's disappearance and murder, according to the prosecutors.
The panel came to the conclusion despite having reviewed evidence which included a DNA test of the skull fragments believed to be Porlajee's, which the DSI insisted was a match to his mother's DNA.
Prosecutors felt more information and evidence was needed to support the DSI's investigation. In the meantime, they have dropped the most serious charge of murder against Mr Chaiwat and the three others.
