An act of revenge that casts a shadow over the future

Until teatime last night the big political question in Belfast was whether Tony Blair and Bertie Ahern could painstakingly lay the foundations for a political breakthrough when they met in Northern Ireland tomorrow.

But in an instant, when the news came through of a death in Donegal, two other questions superseded it: who had killed Denis Donaldson, and how much of a peace process would be left.

In republican terms, Donaldson had brought eternal shame and ignominy on himself with his acknowledgement in December that for 20 years he had been a paid Special Branch informer.

This came to light in a bizarre episode, in which he was charged with running an IRA spying operation on politicians. The charges were eventually dropped, with republicans triumphantly proclaiming that any spy ring had been the work not of the IRA but of British spooks.

Within days, however, the news leaked out that Donaldson was an informer: his confirmation of this sent shock waves through Sinn Fein and the IRA.

The most likely explanation is that Donaldson had withheld from police the fact that he had been tasked by the IRA to run a spy ring. When this was discovered his status as an informer did not prevent his prosecution. His confession was followed by tough questioning by Sinn Fein, and he seemed to have co-operated fully with his interrogators, giving details of his dealings with Special Branch.

Within a few days an understanding seemed to emerge. He would not be shot as so many had been before him. His family was cleared of informing, while he was to get lost and keep quiet.

Until he was tracked down by an Irish newspaper, most assumed he had left Ireland. But he went to ground in Donegal, where he was almost bound to be discovered at some point: he himself seemed to say that the Irish police knew where he was, and many republicans live or holiday in Donegal.

Perhaps he was shot by individuals who were in the IRA with him and who blame him for terms of imprisonment which they and others served. Perhaps the IRA shot him, though the organisation would be acutely aware that doing so would grievously harm its own credibility. Last year it announced it had decommissioned all arms and had in effect wound itself up. Decommissioning, which caused republicans much pain, was partly motivated by the desire to persuade Unionists to form a coalition with Sinn Fein and get republican hands on some of the levers of power in Belfast.

IRA responsibility would also ensure that the Rev Ian Paisley would turn his back on the idea of joint government with Sinn Fein: he has made it clear that he will share power only if the IRA goes out of business.

London and Dublin will therefore be hoping the IRA's leadership did not order or permit the brutal killing of Denis Donaldson, and that this can be demonstrated. If the IRA is seen to be responsible, or suspected of involvement, hopes of underpinning the peace process with a political settlement will be dashed for the foreseeable future.