The Department of Special Investigation (DSI) is expected to seek an arrest warrant for suspects allegedly involved in witness tampering on Monday, relating to the kidnapping and murder of Karen community rights activist Porlajee “Billy” Rakchongcharoen.

An informed DSI source told Thai PBS today (Sunday) that DSI officials found that some officials may have abused their authority by attempting to intimidate witnesses in the case.

The source declined, however, to name the suspects for whom warrants are being sought.

Billy was last seen on April 17th, 2014 when he was arrested by Kaeng Krachan national park officials in Phetchaburi province for collecting wild honey in the park. Led by then park chief, Mr. Chaiwat Limlikhit-arsorn, officials claimed they had released the activist on the same day, but he has not been seen since.

In May this year the DSI took over the investigation of the case and found a 200-litre oil drum submerged in the river near the hanging bridge in the Kaeng Krachan national park.

Burned bone fragments were found inside the drum, which were sent for DNA testing and the relevant parts of the DNA matched Billy’s mother.

Several former park officials, including Chaiwat, were questioned by DSI officials, but no formal charges have yet been filed.

Source