This week marks the 15th anniversary of the Omagh bombing, described at the time by Tony Blair as "an appalling act of savagery and evil". Quite apart from the fact that 31 people died as a result of the attack - including two unborn children - and approximately 220 were injured, what singled out this terrible act of terrorism from so many others in Northern Ireland was the fact that it took place only weeks after the Good Friday Agreement, and in defiance of the peace process that it heralded.