Pinnapha Phrueksapan, widow of ethnic Karen leader "Billy" Por Cha Lee Rakcharoen, stands beside his portrait following a ceremony in Bangkok in September 2019
Pinnapha Phrueksapan, widow of ethnic Karen leader "Billy" Por Cha Lee Rakcharoen, stands beside his portrait following a ceremony in Bangkok in September 2019 AFP / Joe Freeman

Thailand has issued an arrest warrant for a park official implicated in the disappearance of an activist more than five years ago, a rare reversal months after the discovery of the victim's charred remains shed new light on the case.

Ethnic Karen leader Por Cha Lee Rakcharoen -- known as Billy -- went missing in April 2014 while working on a lawsuit accusing officials of destroying homes in Kaeng Krachan national park.

The park chief at the time, Chaiwat Limlikitaksor, was one of the last people to see him alive, after Billy was detained for apparently collecting honey illegally.

At the time Chaiwat insisted he let him go and has denied any involvement in his disappearance. He was later moved to run a larger national park.

But Thailand's corruption court on Monday approved arrest warrants for Chaiwat and three other park officials on charges including premeditated murder, detention and robbery, the Department of Special Investigation said.

Premeditated murder carries the death sentence in Thailand.

When contacted by AFP, Chaiwat sounded calm and said he planned to turn himself in on Tuesday.

"The legal process will start, now not one person will say one thing and another say another thing."

The warrants are the latest dramatic development in a case that has haunted family members.

In April divers found a burnt fragment of a skull stuffed in an oil drum in a reservoir inside the park.

Forensic tests established it belonged to Billy, confirming the worst fears of his widow and five children.

At a tearful memorial in September, the family expressed hope justice would be served by the Department of Special Investigation, Thailand's equivalent of the FBI.

Rights groups say Billy's case sweeps across several problems plaguing activists in the country, including impunity for forced disappearances, environmental destruction and the rights of indigenous groups.

Billy was Karen, an ethnic minority from eastern Myanmar many of whom fled military abuses for neighbouring Thailand.

Thailand is among the most deadly places in Asia for environmental and rights defenders and the United Nations has counted over 80 cases of disappearances in the country since 1980.

tp/joe/fox