Even by the grim standards of Pakistan's recent years, these are dark days. The murder of the governor of Punjab, Salmaan Taseer, an outspoken opponent of the country's draconian blasphemy laws, is not only a shocking event in itself. It also removes from the public stage one of the few men in high office who was prepared to stand up for what he believed in and call for these odious laws to be reformed. Now it is clearer than ever the price that can be paid by those who are ready to take on extreme Islamists. Mr Taseer's successor as governor may be less willing to be so forthright in confronting the clerics and their many supporters.

The fact that Mr Taseer was murdered by a member of an elite police squad should not come as a surprise. For years it has been apparent that religious extremists have penetrated the security apparatus in Pakistan, greatly hampering the government in its oft-stated intention to tackle violent Islamist groups in the country and Taliban fighters on the northern border near Afghanistan.

The governor's death is especially bad news for supporters of Asia Bib, the imprisoned Pakistani Christian whose plight helped to bring the question of the blasphemy laws to the forefront.

It is widely believed that Ms Bibi, who may soon have the horrible distinction of becoming the first woman in Pakistan to be put to death under the blasphemy laws, was arrested and sentenced on trumped-up charges – the victim of a petty vendetta waged by her neighbours as the result of a squabble over water. Significantly, Mr Taseer had recently urged President Zardari to pardon her.

Mr Zardari, whose own wife, Benazir Bhutto, was gunned down in 2007, will probably think twice about that now, presuming that he was prepared to heed the governor inthe first place. The killing is bad news for another reason. Punjab is the heart of Pakistan, and until relatively recently the province looked set to remain free of the kind of sectarian furies that have long tormented the country's unstable fringe. If that is no longer the case, Pakistan's downward spiral will be confirmed.