A VIETNAMESE boat person who wants to go home to be with his ailing mother yesterday fought in the High Court moves to prevent him leaving until he gives evidence as a defence witness at a murder trial. Pham Si Dung, who is represented by Philip Dykes, is required by a defendant to be his alibi witness. But Pham, who has sought voluntary repatriation to Vietnam to be with his mother, is fighting an attempt by the Attorney-General to keep him in the territory until he can testify. A High Court application made by Senior Assistant Crown Prosecutor Steve Bailey on behalf of the Attorney-General said Pham was needed to secure a fair trial for the defendant. Mr Bailey said there was no other practical means of ensuring the witness stayed other than through a detention order from the High Court. Mr Justice Kaplan asked if it was possible to release Pham into the Hongkong community since he had not committed any offence, and repatriate him after he testified. But Mr Bailey said there was a risk of Pham absconding as his priority was to go back toVietnam. The court was told there were 36 defence witnesses and 56 Crown witnesses being detained to give evidence at various trials. Some were detained against their will under court order. Including dependants, about 200 people were involved. Mr Dykes argued that the power given to the Attorney-General to seek an order was exercisable only where the detainee was to be called as a witness for the prosecution and not the defence. Counsel said this application by the Attorney-General was as a third party who had no standing to seek an order. Mr Dykes also argued against the indefinite period of detention, saying there was no indication of when Pham might be expected to testify. It was further argued that Pham was entitled to the protection of the Bill of Rights on the basis that he could not be made the subject of an arbitrary order of detention. If a detention order was to be made under the Immigration Ordinance, it must be demonstrated to be a necessary order, Mr Dykes said. Pham came to Hongkong on July 25, 1991. In February this year he applied to return home. The hearing continues.