POLICE are to offer a cash reward for help in capturing the Tuen Mun rapist, although the amount available has yet to be set, it was revealed yesterday. Police believe one man is responsible for five rapes and two murders in three Tuen Mun housing estates, and the decision to offer cash for information is seen as a concession to residents who petitioned the Commissioner of Police, Mr Li Kwan-ha, over the weekend to issue the reward. The rapist's latest victim was 23-year-old disc jockey Ms Mak Siu-han who was killed in the early hours of April 14 in the stairwell of Hing Sing House on Tai Hing Estate. Senior Superintendent Martin Cowley of the New Territories North district crime units, said: ''Cash rewards are a must in most of these cases. We are working very hard in trying to solve the case, but we can always use a bit of help.'' Mr Cowley said the District Crime Unit 2 would continue questioning residents throughout the early hours and extend that to include daylight hours. ''There are certain lines of questioning to be followed which would help us cover every possible angle,'' he said. Despite reassurances from police that patrols would be maximised, Tuen Mun district board member Mrs Choi Cheung Yuet-lan said yesterday that residents were so worried many were planning to move elsewhere. ''It is understood that the Housing Department would offer families of victims the opportunity to move to other estates, to help put things behind them by starting new lives among strangers,'' Mrs Choi said. Housing Department officials confirmed that four of the six victims' families had asked to move with two requests arranged, one being processed and one withdrawn by the family. Officials, however, strongly denied any increasing incidents of moving from Tuen Mun estates. Mrs Choi and residents' representatives will meet Assistant Director for Housing, Mr Issac Siu Chi-wing, on Thursday to push for installation of closed circuit televisions, iron grilles and deployment of full-time watchmen at lift lobbies on Tuen Mun housing estates. Additional police patrols are being mounted throughout the estates, with regular officers backed up by a police tactical unit, according to officials. The investigation team has set up a hotline for callers with any information related to the cases. The number to call is 666-4320.