The killings illustrate the downside of one-woman brothels, a prevailing form of prostitution within Hong Kong's legal limits. Due to their relative isolation and invisibility, sex workers in these brothels can - and do - fall prey to violence, robbery and even murder.

Yet, to legalise the sex industry, as it is practised in other countries, still needs to be thoroughly debated. The viability of this model has to be considered within context: Hong Kong is facing an influx of migrant sex workers - most of them from the mainland, on tourist visas.

It has been estimated that more than 10,000 mainland women have been arrested, prosecuted and sentenced in Hong Kong from 2001 to 2006; many of them were involved in criminal and/or immigration offences related to sex work. And it is reckoned that Hong Kong's female prison population has expanded beyond the capacity of the government facilities.

Moreover, these figures do not take into account those who are able to evade detection, or those who arrived in the city legally, with work permits, and who are employed as hostesses in restaurants or entertainers in karaoke bars.

The massive shift in prostitution trends since the 1990s illustrates the impact of the influx of migrant sex workers. The price of going to a prostitute has dipped, from more than HK$400, to an average of HK$200, in one-woman brothels.

Yet, owing to their short stays in Hong Kong and the high cost of a visa - estimated at between 10,000 yuan and 20,000 yuan (HK$11,000-HK$22,000) for a three-month visa - migrant sex workers are willing to work from morning until night while tolerating exploitation and abuse. This results in cutthroat competition and an increased propensity for risk-taking for both local and migrant sex workers.

Thus, legalising the sex industry may not be a viable solution. Legalisation implies that local sex workers would have to pay licensing fees, taxes and for medical examinations.

This added burden for local prostitutes would further increase the lure of underground sex workers. Meanwhile, it could send the wrong signal to owners of restaurants and karaoke bars involved in human trafficking. As their profitability increases, so would the burden on the law-enforcement agencies.

In fact, the increasingly blurred border between Hong Kong and the mainland already makes the preservation of law and order within the special administrative region extremely challenging.

The huge income disparity between Hong Kong residents and those from poor mainland provinces means that more women will take risks for financial gain while they stay here.

Moreover, legalisation may cause jitters among ordinary citizens who are not yet ready to see the sex industry move beyond a very limited scope.

Though tragic, the recent killings have at least raised public awareness of the poor conditions endured by sex workers. The incidents have also prompted sex workers to adopt self-defence measures.

While the public, activists and the government all need to share responsibility to effectively protect sex workers as a marginalised group, the huge leap to a legalised industry can only come after careful deliberation.

Kitty Poon, an assistant professor at the Hong Kong Polytechnic University, is author of The Political Future of Hong Kong