The alleged perpetrator of the 2005 Revenue Tower murder rode the building's lift hunting for a target until he met the Thai tourist who was later found dead on top of a ventilation duct, a court heard yesterday. The murder trial of air-conditioning workman So Kam-tong, 27, was told that he had asked one of his best friends, Kwok Chi-fai, to help him hide the body and that he had told Kwok how the attack occurred. Kwok, also 27, testified under immunity against So in the Court of First Instance yesterday. He had known So for more than 10 years - the two went to the same secondary school and worked together in 2005. The prosecution gave Kwok immunity from his involvement in preventing the lawful burial of 40-year-old Charitar Kamolnoranath, believed murdered at Revenue Tower between October 12 and 15, 2005. Her body was discovered on top of an air duct in an 'air-handling room' on the 33rd floor of Revenue Tower in Wan Chai by an electrician on October 24, 2005. She had been missing since October 12. Multiple bruises were found on her decomposed body, and there was a stab wound near her right armpit. Both her hands were tied behind her back with plastic strips. So was arrested on June 6, 2008, after an extensive police investigation. He pleaded not guilty to the murder on Monday. So had described to Kwok how he attacked Charitar and 'accidentally' injured her, Kwok said yesterday. Kwok said So recounted the incident over a meal and So showed him a diamond ring and mobile phone. '[So] told me the items belonged to the deceased woman,' Kwok said. 'He told me he was inside a lift waiting for a target that day... He had worn a pair of trousers with large pockets on each side which could hold a knife. '[So] went up and down in the same lift, waiting for his target. After a while, he met his target,' Kwok said, adding the attack took place after a third person got out of the lift. So dragged the struggling victim to the air-handling room as she stepped out of the lift, Kwok said. 'According to what [So] told me, he accidentally injured her. He then asked her for her credit card PIN,' Kwok said. So went to Tai Wo Shopping Centre that evening to withdraw money from the card at an ATM, but the PIN was wrong, Kwok said. So returned to Revenue Tower but the woman was dead, Kwok said. 'He told me he had taken the victim's money, card, mobile phone and a ring,' Kwok said, adding that So told him the ring had been sold for 'several tens of dollars'. Kwok said he was asked to do some work at Revenue Tower the day before his birthday on October 17 by So. Kwok saw the body, covered in newspaper, on the floor of the air-handling room, he said. He said So took out a knife and put it on the floor, then uncovered the body. The head was wrapped in a red plastic bag knotted under her chin. So signalled for him to help move the corpse onto a higher duct hanging from the ceiling, Kwok said. They later returned to check if So had left anything behind but did not go into the room as there was a workman inside, Kwok said. Kwok waited on the ground floor while So tried again. 'He said something had happened and the police were at the scene.' Kwok said he helped So to move the body because he was afraid that So had a weapon and he had no way to escape from the room. Kwok will continue to testify before Madam Justice Clare-Marie Beeson today.