Raped by an Angel 4: The Rapist's Union(1999)

Overview:

CIA agent turned sexual predator Daniel (Ben Ng) uses his wealth and collection of high-tech gadgets to prey on unsuspecting women. After arranging for the prison breakout of notorious rapists "Rain Killer" (Ankee Leung) and "Tuen Mun Rapist" (Chan Chi-Fai), Daniel invites the men to ravage the two women he has chained in the basement. He next sets his sights on Kwan Shi-han (Suki Kwan), the romance novelist next door; but first preys on her movie star friend, Icy (Yeung Fan). Desperate for a lead, the police consult a semi-reformed deviant known as "The Human Milk Drinking Doctor" (Anthony Wong), who used to prey on lactating women and now controls his sexual urges by working as a porno theatre projectionist.