Supporters of the Swiss environmental activist, Bruno Manser, have given up hope of finding him alive. They said on Thursday he had probably died after returning to Borneo in May to campaign against logging in rain forests.
Malaysian police say there is no evidence that Manser, who was deported last year and barred from re-entering, was in the country.
But the Bruno Manser Fund (BMF) insist he crossed into Sarawak state from Kalimantan, the Indonesian part of Borneo, before disappearing.
"We are resigned," said BMF Secretary John Kuenzli. "If Bruno Manser were still alive, he would have been found."
He said that Sarawak's Penan nomads, whose cause Manser championed, have found no trace of the 47-year-old activist.
In July, the Malaysian prime minister, Mahathir Mohamad, described Manser as a fanatic with a hidden agenda. He has long been a thorn in the side of the local timber industry.
Kuenzli said that if Manser had met with an accident, his remains were unlikely to be found after months in the rain forest. However, he said efforts were being made to find Manser's equipment.
Kuenzli said the suspicion of murder would arise if no gear was found. "We want to have clarity above all," he added.
swissinfo with agencies