By Jonathan Kent
BBC correspondent in Kuala Lumpur
A reward of more than US$15,000 has been offered for information leading to the arrest and conviction of the killers of three young orang-utans in east Malaysia.
Conservationists fear Asia's only great ape faces extinction in 20-30 years
The apes were speared to death earlier this week at a hotel resort in the state of Sabah, where they were undergoing a rehabilitation programme.
There has been considerable shock in Malaysia about the apparently motiveless killings.
The orang-utans were among a group of five attacked at a nature reserve and resort near the city of Kota Kinabalu.
It runs a programme to help orphaned apes return to the wild.
The two who survived are being treated at one of the region's leading orang-utans centres at Sepilok, also in Sabah.
The resort has offered a reward for information leading to the capture of those responsible, as has a British circus which is currently performing there.
Police have set up a task force to carry out the investigation.
Two former employees of the resort were arrested, but later released.
The World Wide Fund for Nature puts the number of orang-utans left in the wild at fewer than 25,000, a tenth of what it was a century ago.
The population is spread between the Indonesian island of Sumatra and the island of Borneo, of which Sabah is a part.
The populations are under pressure because the tropical rain forests in which they live are being felled, primarily to make way for palm oil plantations and subsistence farming.
Malaysia has sought to stop the destruction of their habitat in recent years, but many young orang-utans are rescued from poachers who try to sell them as pets, often after killing the apes' parents.