IF there is ever a new court building constructed in Britain the architects should think twice before installing the traditional figure of Lady Justice.

By convention she stands blindfolded, the better to remain impartial before the evidence. It is a classical, old-fashioned interpretation. Today, Justice is more likely to take the form of a clear-eyed relative, a wife, a mother, a husband, a father, who is determined to stare down authority until the truth emerges.

The latest such individuals seeking justice are the Finucane family. In 1989, Geraldine Finucane's husband, a Belfast solicitor and father of their three children, was murdered by a hit squad from the Ulster Defence Association. The killing took place in the family's home as they sat down for Sunday dinner, the terrorists using a sledgehammer to batter their way in. As the shots rang out, blast after blast after blast, the children clung to each other, terrified. Even by the grisly standards of Northern Ireland's dirty war, the scum with guns had sunk to a new low.

This week, a new report on the murder confirmed that the wrongdoing did not begin or end on that day. Over the course of 800 pages, Sir Desmond de Silva, the review's author, demonstrated beyond doubt that collusion between the British state (the Army, the Royal Ulster Constabulary special branch and security services) and loyalist paramilitaries resulted in the murder. Thereafter, there was "a relentless attempt to defeat the ends of justice" in covering up the collusion.

No wonder the House of Commons fell silent as David Cameron delivered the findings of the review on Wednesday. As he has shown several times during his premiership, Mr Cameron has the ability to rise to the occasion when the occasion demands it. This was one such moment. "It is really shocking that this happened in our country," said the Prime Minister.

Mrs Finucane did not look shocked when she later condemned the report as a "whitewash" and a "confidence trick". Mrs Finucane looked beyond weary, but she was not giving up. Looking straight into the camera lenses, she said her fight for a full, independent, public inquiry would continue. It was a blistering look, at once full of dignity and cold, clean, righteous fury, the kind of look worn by Doreen Lawrence, the Hillsborough families, and too many others bone-tired with injustice. It was the look that said: "I am fighting on, because the ones that have gone cannot do so". It was a look that should have made Mr Cameron reconsider his decision not to set up a public inquiry.

Mr Cameron was right to be shocked by the report. It was the sort of crime and cover-up that would not have been out of place in the grimmest days of Latin America's grubby wars. A lawyer killed for doing his job. A killing contracted out by the state. A cover-up that was so outrageously, insultingly, blatant. Had this occurred in Washington DC rather than Belfast there would have been a million-lawyer march on the Capitol for a start. Here? An apology by the Prime Minister, much shaking of heads in dismay, some column inches in the papers, minutes on the news, but in most outlets not the main story. That, in its own way, is shocking too.

It is perhaps not that surprising, however. When it comes to Northern Ireland, different standards have always been applied. The rule book, as the de Silva and many another report has shown, went into the shredder early on. Northern Ireland was different, went the argument. There was a war going on and there were casualties and atrocities on both sides. This wasn't apartheid South Africa, truth and reconciliation were never going to happen in that place. Too much truth, indeed, could be fatal to the peace process. It is bad enough what is known already; imagine if all the scabs were ripped off, how much poison would flow then, would the body politic stand a chance of recovery?

Looking at Northern Ireland from week to week, one can begin to have some sympathy, albeit misguided, for the view that the past is a foreign country that should be visited only when absolutely necessary. History? Northern Ireland has had a bellyful of the stuff. As have the countries closely associated with it, Scotland among them.

Even the present can be a tricky customer. Take the rioting and death threats which have followed Belfast City Council's decision to fly the Union flag on designated days only. Though what has happened politically in Northern Ireland has been nothing short of miraculous, it does not take much to show that peace overall is of the distinctly uneasy kind.

There is the cost and duration of another public inquiry to consider, too. The Saville Inquiry into Bloody Sunday took 12 years to complete and cost £195 million. There has already been a four-year inquiry into the Finucane case, resulting in an official report by Sir John Stevens in 2003, and another inquiry into collusion by Mr Justice Cory, a Canadian judge. Is it not the case, as the British Government argues, that all that is going to be uncovered has been uncovered?

We simply do not know for certain, and that is the point. For all Sir Desmond's report was shocking in the way it exposed the behaviour of state agencies, a lot of this information had already been placed in the public domain. The review was held behind closed doors and, most critical of all, those interviewed were not cross-examined. When it comes to letting daylight in, this is like putting a pin hole in an oak door and allowing people to peer through. You cannot see what lurks in the corners, but you will just have to trust that it is not relevant.

Not relevant, or too dangerous to know? That, again, we don't know. But we do know what will happen if there is no public inquiry. The doubts, fears and suspicions will fester. The stench of justice denied will not go away. As for questions of cost, can it really be acceptable to spend £5m on an inquiry into phone hacking, but not do the same when it comes to the state-facilitated murder of a lawyer?

The Finucane murder was not just another case, it was not just another murky episode in a fogbound war. This attack on a lawyer was an attack on democracy. If all those responsible are not held to account, Lady Justice might as well add earplugs and a gag to that blindfold.