Hong Kong takes pride in its reputation as a place where the rule of law is paramount. This is a society where people can walk the streets and speak their minds without fear of attack and where violent crime is rarer than in most cities. That is one reason why yesterday's brutal attack on talk show host Albert Cheng King-hon sent such shockwaves through the community. While it is impossible to be sure of the motives of his assailants, it is not unreasonable to suspect they may be related to something Mr Cheng said in his role as one of the community's most outspoken commentators. If that is so, this constitutes a challenge to freedom of expression as well as to the rule of law. The SAR has few enough prominent personalities who are prepared to speak their minds without fear of the consequences. They may make life uncomfortable for civil servants and other leaders who are the victims of their criticism. But the huge popularity of Cheng's programmes demonstrates the vital role that such outspoken commentators play in stimulating the lively debate that is one of the bedrocks of Hong Kong's way of life. It would be doubly tragic if yesterday's assault were to stifle this freedom. But there is certainly an understandable danger of other critical commentators becoming more reluctant to speak out, especially about those criminal groups who have been traditionally linked to chopping attacks. The past few years have seen a alarming increase in violence against media personalities. From fire-bombing and vandalism to the assault that severed the arm of publisher Leung Tin-wai there has been a growing trend towards settling grievances with the media through violence rather than rational discussion. Early yesterday, two men attacked a reporting team to warn them off covering Shenzhen. Worse still, those responsible are never caught, despite a $3.8 million reward in Mr Leung's case. There is often very little to go on. Even if the actual assailants can be found, it would be almost impossible to identify those behind them. But this latest outrage shows that greater efforts must be made, perhaps through better use of police intelligence on criminal groups. A cloud now hangs over the rule of law and freedom of expression. It will only be lifted when those responsible for this cowardly attack are brought to justice.