Today should be an occasion for satisfaction for the relatives of those who died on Bloody Sunday: their long battle for a new inquiry ends with the opening of hearings in Derry this morning. But the occasion has been marred by a wrangle about legal representation which may mean that at least some of the families will not co-operate with the inquiry.

The first item to be discussed by the inquiry, chaired by Lord Saville, is entitlement to legal representation. The families are deeply dissatisfied with the offer from the tribunal of just a single legal team to represent them all and handle all aspects of their case.

Faced with the might of the British military and political establishment, they feel they need a formidable legal team and access to independent experts to bring to light, at last, what happened on Sunday January 30th, 1972.

For the 10,000 or so anti-internment demonstrators in Derry that day, and for the journalists and others observing the demonstration, it was always clear what had happened - the demonstration was penned in by the British army and then fired on by members of the First Battalion Parachute Regiment, which killed 13 people, eight of them teenagers, and wounded another 14, including one man who died later from his injuries.

Ignoring calls for an international inquiry, the British government moved within days to set up its own tribunal under the chairmanship of Lord Widgery, the Lord Chief Justice and a former army officer. This inquiry served to compound the devastation felt by the community in Derry as a result of the shootings.

From the start the Widgery Tribunal was regarded with mistrust by the community in Derry.

These reservations were vindicated when his report effectively ignored the evidence of the civilian witnesses, along with that of the 21 journalists and photographers and seven priests who appeared before him. Instead, it supported the contention of the 48 soldiers and members of the RUC, who claimed they were fired on as they entered the Bogside.

That allegation - that some of the demonstrators had fired guns and hurled blast bombs - was offered by Lord Widgery as a justification for the troops firing on the demonstrators. No evidence was found to suggest that any of those killed had been armed, but this did not deter Lord Widgery from concluding: "None of the deceased or wounded is proved to have been shot whilst handling a firearm or bob. Some are wholly acquitted of complicity in such action; but there is a strong suspicion that some others had been firing weapons or handling bombs in the course of the afternoon and that yet others had been closely supporting them."

In Derry the report was met with fury. The families of the victims had their grief intensified by the suggestion that their loved ones had brought it on themselves. Since then they have campaigned to clear the names of those who died, to win acknowledgment that they were the innocent victims of unjustified action by the British army.

For over two decades, that campaign was a muted affair, hampered by lack of resources and battling against a gradual loss of interest.

Some family members of those killed have marched on annual commemorations of Bloody Sunday organised by Sinn Fein; others tried to keep their quest for the truth outside the realm of party politics. Bishop Edward Daly, who as a priest had attended to the dead and dying, along with the local MP, John Hume, badgered the British government for an acknowledgment of the truth and an apology.

The first grudging and partial recognition of the innocence of the victims came from John Major in December 1992, when he wrote to Mr Hume: "The Government made it clear in 1974 that those who were killed on `Bloody Sunday' should be regarded as innocent of any allegation that they were shot whilst handling firearms or explosives. I hope that the families of those who died will accept that assurance."

The 25th anniversary of the shootings in January last year revived interest and gave impetus to the search for fresh evidence. Significant new evidence was uncovered.

Perhaps the most important was the book edited by Don Mullan, who was a boy of 15 in Derry on Bloody Sunday. Following the shootings he, along with hundreds of others, gave a statement to the Northern Ireland Civil Rights Association.

His curiosity about this statement was aroused by a chance meeting with Tony Doherty, the son of one of the victims. He found several hundred of these eye-witness statements in a plastic bag in the office of the Derry-based human rights organisation, the Pat Finucane Centre.

He determined to see the statements published, and edited a selection which was published, with a lengthy introduction containing much new information, in January 1997.

The book had a significance beyond the vivid recollection of the events by participants. As Don Mullan read the statements a startling new realisation struck him - in addition to members of the Parachute Regiment firing live ammunition from ground level, another regiment of the British army had been firing from the Derry walls.

Such a possibility had already been raised by the Derry GP who had attended many of the dying and wounded, Dr Raymond McClean, and who had written a book on Bloody Sunday some ten years earlier. His post-mortem reports appeared in an index there, and in three the trajectory of the bullets was noted as "from the front, travelling backward and downward". No one had seen that as significant before.

Mr Mullan found an experienced ballistics expert in the US who concluded that three of the victims had been shot from the city walls. Last January, Channel Four News published interviews with soldiers who were present which further supported this theory.

Further new evidence emerged - the statements given by the soldiers to the military police after the shootings. Prof Dermot Walsh of Limerick University analysed the differences between them and the statements they gave to the Widgery Tribunal and found discrepancies which suggested they had been coached in their evidence to the inquiry.

The campaign for a fresh inquiry received a huge boost, and the then Taoiseach, Mr Bruton, called for a new investigation on January 29th, the eve of the 25th anniversary. The Government began to compile its own evidence.

With the election of the Labour government in Britain, hopes for a fresh inquiry rose. On June 3rd last year, the Northern Secretary, Dr Mo Mowlam, met the families of the victims.

But progress was slow. Eventually, on the eve of the 26th anniversary of Bloody Sunday, Mr Blair announced a fresh inquiry with the words, "the weight of evidence now available is such that these events require re-examination". The Irish Government published its report the same day.

For the families, there must be no dismissal of the available evidence this time, and no fudging of conclusions based on it. They are sure they can contest the version of events accepted by Widgery. But for this they maintain that they need the professional help of their own lawyers and their own experts. Their trust in today's inquiry depends on whether they can get them.