In April 2014, rangers detained Pholachi “Billy” Rakchongcharoen in Kaeng Krachan National Park, southwest of the capital of Bangkok, but he never appeared at a police station for processing and has not been seen since.

He had been working to protect the rights of members of his ethnic Karen community who had been evicted from the park.

On Thursday, a Bangkok court sentenced National Parks chief Chaiwat Limlikit-aksorn to three years in jail for failing to properly charge Pholachi in 2014. But murder charges against Chaiwat and three other officials were dismissed.

In a statement, the court added that DNA tests of bone fragments discovered by investigators in a scorched oil drum dumped in the national park were not enough to prove the bones belonged to Pholachi, even though they matched a sample taken from Pholachi’s mother.

It also said there was not enough evidence to determine that he was murdered.

Chaiwat was granted bail and plans to appeal the sentence, domestic media said.

Reuters could not reach Chaiwat or his lawyer to seek comment.

Pholachi’s disappearance is one of more than 80 such instances of enforced disappearances in Thailand since 1980, rights groups says.

(Reporting by Panu Wongcha-um, Panarat Thepgumpanat; Editing by Clarence Fernandez)