At least two sex predators who tried to rape two teenage girls and indecently assaulted two others in Chai Wan over the last few months have become the quarry of a police ambush prompted by fears that they will strike again.
The attackers are still on the loose since the four girls fell prey to them in December and April at public housing estates.
"From our experience, sex offenders usually repeat their offences and strike in the same area or nearby," a police source said.
Officers are understood to be monitoring Fung Wah and Hing Wah estates, where the four incidents took place. Beat policemen have also stepped up round-the-clock patrols.
A four-member task force has been formed to join the Eastern district crime squad in poring over hundreds of closed-circuit television tapes.
And officers from the Police Tactical Unit are helping investigators carry out door-to-door inquiries at thousands of households on the two estates.
"We believe the sex attackers are familiar with the areas where they struck," the source said. "They may be living in the estates or are former residents."
DNA tests are under way on the clothes the four victims wore at the time of the attacks. Officers are also checking whether descriptions of the attackers match former sex offenders.
"We are very concerned that the attacks pose a threat to public safety," the source said. "We are looking into all possible clues."
The two attempted rape cases occurred within a week in December. Officers believe both attacks were carried out by the same man, a Cantonese speaker.
The two reports of indecent assault happened on the same day in April. Police are checking whether the same man was behind both attacks. So far, no arrests have been made.
In the first attack, on December 13, a 15-year-old girl had a lucky escape at a basketball court near Fung Wah estate at about 10pm. The attacker had subdued her and pulled down his underwear, according to a police investigator. "She begged him and managed to persuade him to let her go," he said.
She went to the police a day after another girl, 16, was attacked at the same site on December 18. The second girl was rescued when a passer-by shouted for help.
The force has issued a sketch of the suspect. He is believed to be 20 to 30 years old, about 1.75 metres tall and of thin build.
In the April 8 incidents, a man threatened the two girls, aged 14 and 17, with a box cutter and indecently assaulted them nine hours apart in broad daylight on Hing Wah estate.
A jobless man was on April 8 jailed for 15 years, including 10 years - the maximum penalty - for indecent assault. Cheung Man-wai, 35, grabbed his 14-year-old victim from behind on a Tai Po street, robbed her, led her to a hillside, stripped, molested and violently assaulted her.
The city saw a 13 per cent drop in rape reports to 105 last year from 121 in 2012. There were 1,463 reports of indecent assault last year, a 2.1 per cent drop from 1,495 in 2012.