"This case is actually very significant," said Edwin Wiek, director of the Wildlife Friends Rescue Center that treats abused animals near Bangkok.

"We've had cases of seven or eight chimpanzees being smuggled, but there's never been a case so big. Over a hundred orangutan found only in one place," he said.

Experts say the DNA testing will pinpoint the birthplace of the orangutan to within a few hundred kilometers (miles) in an investigation reaching a climax as Thailand prepares to host an international environment conference in October.

If the orangutan are found to be from Indonesia, they will be repatriated and the owners of the Safari World amusement park would be prosecuted, police say.

The owners of Safari World said initially their 115 orangutan were a result of a successful breeding program, but have now admitted buying a number of them illegally, police investigator Aroon Promphanapes told Reuters.

"The owners said they got 45 of the orangutan through an exchange with someone in Thailand. Who they made the deal with and what they exchanged for the animals, we do not know yet," he said.

The DNA results should be known in about a month, when hundreds of delegates meet in Bangkok for the Convention on the International Trade in Endangered Species (CITES) conference.

"I think we should really consider for the future how these cases are dealt with," Wiek said.

"In the 10 months that this case has been going, the animals are still in the same place, 13 of them have died in circumstances we don't know about and I'm really concerned about the welfare of these animals," he said.

Indonesia has also expressed concern for the animals with protesters demonstrating outside the Thai embassy in Jakarta last month to demand the immediate return of the orangutan.

Fewer than 30,000 orangutan are left in the jungles of Malaysia and Indonesia.

Animal rescue groups have offered to pay for the repatriation of the animals if they are found to have come from Indonesia. The apes will then need to be rehabilitated and released into the wild in a process which could take several years.