By Jonathan Kent
BBC correspondent in Kuala Lumpur
Police in east Malaysia have arrested a man in connection with the killing of three orang-utan.
The orang-utan is at risk of extinction in the next 30 years
The three apes, named Mambo, Terry and Marrie were stabbed to death last week at a resort and nature reserve in the state of Sabah.
Two other orang-utan who were part of the same programme to return rescued animals to the wild, have been treated for injuries they received.
The detained man is a former employee at the nature reserve.
Two former workers at the resort were arrested last week, but later released without charge.
Following their deaths, a reward of US$15,000 was offered for information leading to the conviction of those who carried out the killings.
There has been considerable shock in Malaysia about the apparently motiveless killings.
The World Wide Fund for Nature puts the number of orang-utan 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-utan are rescued from poachers who try to sell them as pets, often after killing the apes' parents.