THE inquiry into the tear-gassing of hundreds of Vietnamese asylum seekers at Whitehead detention centre has been denied the power to summons or grant protection to witnesses or take sworn evidence. The lawyer leading the inquiry, Andrew Li Kwok-nang QC, said the Commissions of Inquiry Ordinance, which gave full judicial powers to commissioners, had not been invoked for the purposes of the Whitehead probe. He said no evidence could be taken under oath and there was no authority available to him to summons people. The threat of perjury for the giving of false evidence is available under the ordinance, but because Mr Li will not have that power, he will have to rely on peoples' honesty when answering. Mr Li said he expected people to co-operate with him and his staff when they sought information. One of his biggest problems would be getting independent, corroborative evidence. Mr Li said he was faced with assessing evidence from Correctional Services Department (CSD) and police officers on one side of the fence and from the Vietnamese on the other side. He said discerning the truth or a middle ground was going to be very difficult given the ''black and white way'' he expected information to be given from the authorities and the Vietnamese migrants. Mr Li, an Executive Council member, will conduct the inquiry with internal medicine expert and fellow justice of the peace, Professor David Todd. The pair have been asked to investigate and report back on a military-style raid conducted at Whitehead on April 7 in which 1,250 police and CSD officers fired 557 canisters of tear-gas to remove 1,500 people from Section 7 of the camp and transfer them to High Island detention centre. A total of 73 people complained of assault by officers in the operation and 272 people sought medical treatment.