HOW do you measure the impact of words that were 38 years in coming? Some have tried to weigh them, noting that Lord Saville’s report on Bloody Sunday is a full 20 kilograms on the scales. Or that it contains 5000 pages in 10 volumes, the fruit of 30 million words of evidence.Others have tried to measure them in time, pointing out that it took 12 years for the law lord to reach his conclusions. Inevitably, others reach for a financial scale, gulping at the more than £190 million ($326 million) price tag.But a better measure might be the human one, starting with the cost not of the inquiry but of the episode itself. The cold facts of January 30, 1972, are so well known that for a while they lost their power to shock. Thirteen civil rights marchers were shot dead on the streets of Londonderry by the British Army; another died later of his injuries.But when you hear again the lasting, human legacy of those facts, the numbness fades. Not the larger consequences – including the view, expressed to me by a veteran republican, that Bloody Sunday all but created the Provisional IRA, as well as fixing Northern Ireland on a path to mayhem and violence that would endure for decades – but the more intimate impact.The death of 17-year-old Michael Kelly, a trainee sewing machine mechanic, becomes more real when you read that his mother was so broken that her family feared letting her out of the house. One day they found her heading up towards the cemetery, clutching a blanket. “I’m going to place it over Michael’s grave to keep him warm,” she said.For the Kelly family, and all those like them, every penny spent by Saville has been worth it. You could see that, written on their faces as they gathered in the sunshine of the Guildhall Square in Derry on Tuesday, fresh from getting their first glimpse of the Saville report, fist-pumping the air and declaring, one after another, in a desperately moving ceremony, that those they had loved and lost had been found innocent.Inevitably, there are complaints that, since 3700 people lost their lives in Northern Ireland’s Troubles, it is unjust that 14 victims have been elevated to a higher rung in the hierarchy of suffering, their murders scrutinised by a full legal inquiry denied to the others. The only answer to that lies in the nature of the killers. For those pulling the trigger were British soldiers acting in the name of the British state, mowing down their fellow citizens. This is what gives Bloody Sunday its singular quality: it represents the biggest single massacre by the British military on British territory since Peterloo in 1819.If the event itself was one of historic proportions, so is the report. It represents a rare admission by the state that it committed a grave wrong. By conceding that the killings were “unjustified and unjustifiable”, and adding that he was “deeply sorry” for them, David Cameron has told the world that Britain killed innocents and, through the whitewash of the 1972 Widgery report, covered up that truth. The Saville findings and Cameron’s statement will take their place alongside Tony Blair’s apology for British culpability in the Irish potato famine of the 19th century: mocked by some, but a step towards a true reckoning with its imperial past.Will it be enough?In one immediate way, it will. What always united the Bloody Sunday families was the urge to see the names of their loved ones cleared. The accusation in the immediate aftermath of the massacre that those killed had been armed terrorists represented a kind of double death. Not only had these men, half of them teenagers, been gunned down, they had also had their reputations destroyed. Saville’s declaration that none of them posed any kind of threat delivered the exoneration that these families craved. For most it came too late: all but one of the parents whose sons were killed that day are now themselves dead.Where the families divide is on the question of what should happen next: should the paratroopers held by Saville to have been out of control, and to have lied about their actions afterwards, be prosecuted, either in a criminal case or a private, civil action? Some say they won’t rest until they see the killers in the dock; others believe they have now had their judgment day, thanks to Lord Saville.The arguments for prosecution are powerful. Murder is murder, no matter who commits the crime. No one is above the law. And, it should be stressed, Saville gave no blanket promise of immunity to the soldiers who came before him.Guardian News & Media