The security forces and the government will fear that the attack was carried out by, or with the assistance of, a major loyalist grouping such as the Ulster Defence Association (UDA).
There have been recent concerns that the UDA, one of the two big loyalist paramilitary outfits, was showing signs of becoming detached from the peace process. The grouping has found itself out in the cold of late, since representatives of its political wing failed to win seats in the Belfast assembly.
The fear has been that without a political anchor it might drift away from the peace process and return to killings.
Loyalists have in recent months been the main source of violence in Northern Ireland. They have carried out roughly the same number of "punishment" attacks as the IRA, and have also petrol-bombed several dozen Catholic homes.
The level of killings has by Northern Ireland standards been low, loyalists have been responsible for three of the four deaths since last September. Two of these were carried out by a small splinter group, the Red Hand Defenders.
But although this group has some guns most of its attacks have been carried out using crude petrol-bombs or pipe-bombs. The question therefore arises of whether it had the capacity to make a device such as that which killed Mrs Nelson. The UDA, however, has in the past used such devices.
There is also a historical pointer towards the UDA in that the organisation was responsible for the killing in 1989 of a solicitor, Pat Finucane, who like Mrs Nelson was viewed as a highly effective advocate for nationalists and republicans.
Mr Finucane's case remains a political issue, with allegations of official collusion gathering ground. Only last month more than a thousand legal figures from all over the world signed a petition calling for an investigation into his death. Last night republicans and nationalists were already alleging security force involvement in Mrs Nelson's murder. Her killing seems destined to join that of Mr Finucane in the annals of the many cases accruing more and more allegations as the years pass.Reuse content