The Peeping Tom.

Roy Chen Chih Lai is a serial rapist and murderer with a leg fetish, and cuts off his victims' legs as trophies after he's through with them. One day at a bank robbery shootout, he catches police woman Cheng Hsuen on camera, and chooses her to be his next victim. He begins to stalk her and enter her personal life, even waiting for her inside her home. He notices her sister, Kelly, as well (who is also a cop), and her boyfriend, Ken. After he kidnaps and rapes Kelly, Cheng decides to lure the madman by using herself as bait, and bring justice to the situation.