If it was the work of the so-called "Real IRA" or the "Continuity Council" then, in their cowardly inhumanity, this splinter group have shown themselves to be worthy successors to all the worst traditions of Republican terrorism. They must be proud of the scale of their slaughter. If the murder of civilians including children and a pregnant woman are what it takes for them to demonstrate that they mean business, then they have surely succeeded. What they have not, and cannot, succeed in is undermining the peace agreement. That is their aim. But if the best hope in a generation is to succeed, then some things necessarily follow.
One politician summed it up admirably: "It is time for us to keep our nerve, it is a time for us to give sensible political leadership, it is a time for us to band together and to show these people that they aren't going to succeed in destroying the peace process." Not the words or John Hume, Mo Mowlam or Tony Blair, but of Sinn Fein's Martin McGuiness. In the days when Mr McGuiness's organisation was on the receiving end of such declarations, he and his colleagues rejected the "politics of condemnation". Well, he should recognise that now too, condemnation of violence by Sinn Fein - novel and valuable though the words may be - is not enough.
There must be some movement on the part of Sinn Fein and the IRA and the other paramilitaries to hand in their weapons. David Trimble was right to renew his call for progress on this front. Perhaps the Omagh bombing would have taken place anyhow. But for every ton of Semtex, for every stashed Armalite, for every bomb factory in the control of the paramilitaries, the less secure and the less stable will Ireland be, and the more difficult it will be for the habits of democracy and civil politics to take root.
In the aftermath of such an outrage, the paramilitaries will be tempted to take the law into their own hands. Well, we have seen quite enough rough injustice on all sides during these Troubles. Those who perpetrated these crimes need to be punished through the rule of law and the courts, on whichever side of the border they are hiding. Sinn Fein and the IRA should co-operate with the authorities to bring those responsible to justice. As we try to look ahead, few developments would help retain confidence in the peace process more.
The people of Northern Ireland have the right to expect that those who are currently being released for terrorist crimes - and some atrocities that at the time shocked and appalled as much as Omagh does now - are really prepared now to work for peace and are not recidivists looking for an easy "get out of jail free" card. There needs to be a closer link between prisoner release and decommissioning of arms. The maximum sensitivity and care must be applied to this process.
The events in Omagh on Saturday are immensely saddening. But we should recognise that it will probably not be the last atrocity in the present Troubles. A tiny group of people have the determination and resources to perpetrate these outrages. They will be difficult to eliminate. But, as with the survival of the peace process after the murder of the Quinn brothers, after the tensions of the marching season and the Banbridge bomb, there is the hope that the carnage, albeit unprecedented in its scale, is, essentially, part of Ulster's past. As Martin McGuiness said, it is time to keep our nerve.