A 13-YEAR-OLD boy found dead in a pump room in a Sha Tin public housing estate yesterday had been tied up with wire and gagged. Hung Siu-chung was found on the rooftop of Chi Wo House, Wo Che Estate, by a 41-year-old female cleaner around 1.30 pm - 30 minutes after his parents reported him missing. The couple told police they were concerned about their son, whom they had not seen since he left home on Monday afternoon. The husband is a senior staff member of the Fire Services Department and the family lives in government quarters nearby. The boy's mother and brother were taken to the pump room and identified Hung's body. Sha Tin Assistant District Commander (Crime) Superintendent Tam Tak-wing said there were no apparent injuries on the body. However, the boy's hands and legs were tied with wire and there was another wire around his neck. His eyes and mouth were covered with adhesive tape. A postmortem examination will be carried out today. Police are investigating access to the pump room as the iron gate to the rooftop should be locked. Police have yet to establish a motive in the case but some residents suspected Hung's death might be related to a recent spate of youth crimes in the area. One 47-year-old housewife said the problem was getting worse and she was anxious about the safety of her two daughters and son, aged between 11 and 20. ''Many teenagers in school uniform gather on the staircase outside my flat having lunch or smoking.'' She said young gangsters had robbed morning walkers and other teenagers on cycle tracks and in the city's gardens. Police appealed to anyone who might have seen someone acting suspiciously on the rooftop of Chi Wo House between 2 pm on Monday and midday yesterday to telephone 694-6308.