Truth surely lies at the bottom of a very deep well, as the proverb has it, and it is being drawn out in very small buckets as the Bloody Sunday Inquiry grinds on in the shadow of Derry's ancient walls.
It is three years this month since the chairman of the tribunal, Lord Mark Saville, made his formal opening statement, and a year since oral hearings of evidence began. It resumes after a break of several weeks on April 30th.
Just as daily events must have swung between crises and calmness during the 105 days of Derry's longest siege, the course of the inquiry has veered frequently from tedium to drama and back again. And it seems clear that some of the most testing episodes lie ahead, even if the protagonists are unlikely to be reduced by starvation.
In the morass of millions of words, thousands of pictures and diagrams, volumes of expert reports and hours of audio and video tape and film, it is easy to lose track of what is at stake. The object of the inquiry is to seek the truth, the chairman has repeatedly said. It is not a trial, and therefore should not be conducted as an adversarial contest, he points out.
But British justice and fair play are, indeed, on trial, in the arena of public opinion, if not by the tribunal itself. And the treatment of witnesses is frequently as abrasive in nature as anything that might be permitted in an adversarial criminal case.
A fundamental purpose of the inquiry is to restore public confidence in the fairness, impartiality and thoroughness of British legal process - concepts which were gravely damaged, especially (though not exclusively) in nationalist Ireland, by the previous inquiry carried out by Lord Widgery in 1972.
The absorbing and all-important question overshadowing this hugely expensive and protracted project is whether a British government-appointed tribunal of inquiry can, if the evidence so accumulates, draw conclusions which may be seriously embarrassing to powerful Establishment interests and highly critical of members of an elite officer class and a crack regiment.
It was the canny George Bernard Shaw who observed: "Truth telling is not compatible with the defence of the realm". And Voltaire surely touched a related nerve with his comment: "Who seeks for truth should be of no country" - except that he might have added: "and of no clan, creed or class".
We must wait another two years at least to see the outcome of this formidable test. Meanwhile, there is no doubt that the very process of the inquiry has a dynamic importance at several levels.
Since the tribunal's own senior counsel, Christopher Clarke QC, completed his marathon, 40-day introductory review of the evidence gathered during the two years of preliminary investigation, close to 200 civilian witnesses have been heard.
Their personal accounts of the terrifying violence unleashed upon them, their friends, neighbours, relatives and fellow civil rights marchers were gripping and at times intensely emotional. There were tears and occasional breakdowns.
Many admitted that this was the first time in 28 years that they had been able to bring themselves to speak in detail of the horror they witnessed at close quarters. Most, in their preliminary sworn statements, spoke of the sense of communal injustice and grievance which led them to join in what they saw as a peaceful protest against the denial of civil rights.
There were core demands for social, economic and political reform which had given rise to the campaign of the Northern Ireland Civil Rights Association (NICRA). But undoubtedly the culminating repressive measure - and the focus of the protest on Bloody Sunday - was the introduction of internment without trial.
On a coldly anatomical scale of assessment, the 29 fatalities caused in the Omagh bombing of 1998 involved much more gruesome physical injuries than Bloody Sunday, as the Omagh inquests painfully revealed. So also did a range of other paramilitary bombings during the Troubles, from Bloody Friday to the Shankill Road.
But the Bloody Sunday killings and woundings were inflicted by agents of the state, in some cases on victims who were face to face with their attackers, and the shooting episode continued over a relatively extended period in the immediate presence of thousands of civilians.
The 60 or so who were arrested, in fact, had to endure a prolonged ordeal for several hours, on their evidence of the sometimes bizarre ritual of threats and ill-treatment carried out by their captors.
We will hear more of this in coming weeks, with several hundred civilian eyewitnesses still to give evidence. Then will follow the hundreds of soldiers, police, experts and politicians who have been lined up to testify.
Already, however, a pattern has unfolded, legal personalities and styles have been fleshed out and various problematic issues identified. Initially, during the questioning of witnesses, both the chairman and the tribunal's counsel pointedly referred to the "wall of silence" encountered in relation to both wings of the IRA, their membership, orders and disposition on Bloody Sunday.
This was cited to justify the tribunal's tolerance of hostile questioning of civilian witnesses. Indeed, when one counsel, Richard Harvey, had the temerity to query the propriety of witnesses being asked to elaborate on rumours and gossip they might have heard, he was shown the sharp edge of the chairman's steel.
Several prominent QCs have led the charge on behalf of the paratroopers and other military witnesses who have yet to take the witness stand, and against whom grave accusations have been laid.
There is the "good cop, bad cop" pairing of Edwin Glasgow and Edmund Lawson which has been to the fore in recent months.
Cambridge-educated Lawson, a rugby enthusiast, bores in like a tenacious prop forward, seeking aggressively to undermine the credibility of some witnesses.
He seems unfazed by the occasional reprimand from the chairman. A female witness was provoked into telling him to "stop badgering me", and once, as he persistently "grilled" another woman, his colleague was moved to prompt him, sotto voce, to "leave it".
Glasgow, on the other hand, an opera and music fan who was decorated with a CBE in 1998, is civility personified. He softly lulls the witness with sympathetic phrases before suddenly confronting them with some apparent inconsistency dredged from a previous statement.
Cardiff-educated and Exeter University graduate, Gerard Elias, joins in regularly as QC for another group of soldiers. But this solemn cricket enthusiast often seems slightly nonplussed when his "googly" fails to find its mark.
The tone of the questioning of witnesses appears to have moderated somewhat since the tribunal made a highly significant breakthrough several weeks ago in relation to IRA participation.
At least five self-acknowledged members of the Official IRA in 1972 are now known to be in contact with the inquiry through legal representatives, with a view to giving evidence. And, after a long period of non-contact, a lawyer for Martin McGuinness of Sinn Fein is in negotiation on the terms and date on which he will testify. More problematic and mysterious is the attitude of the UUP MP, John Taylor, who has apparently failed to respond, up to very recently at least, to all correspondence from the inquiry's solicitors. He is a potentially crucial witness for the political aspects of the tribunal's investigations, as he was chairman of the vital Joint Security Committee meeting at Stormont on January 27th, 1972, just three days before Bloody Sunday.
Little or no detail is publicly known about the discussions at this meeting, which certainly would have discussed security plans and strategy for the handling of the march on January 30th.
It is believed that only four people who attended that meeting are still living. Apart from Taylor, the most important of these as a potential witness for the inquiry is probably Sir Kenneth Bloomfield, one of Northern Ireland's most distinguished and prominent public servants. He celebrated his 70th birthday last week. The other two are the former RUC Chief Constable, Sir Graham Shillington, who has just turned 90, and the former Stormont government security advisor, William Stout, who is now aged 94.
Observers have been somewhat puzzled by the relatively low-key role adopted by lawyers representing the families of Bloody Sunday victims and the wounded during the testimony of civilian witnesses so far.
The speculation is that they have been "keeping their powder dry", so to speak, for their crucial and testing confrontation with the military witnesses at some future stage. But there have been murmurs locally, nonetheless, as the soldiers' counsel appeared to enjoy a "free ride" during their intensive interrogation of civilian witnesses.
At one point, Michael Mansfield QC, felt it incumbent to state that he and colleagues, such as Lord Anthony Gifford QC, Arthur Harvey QC and other counsel, are specifically briefed on behalf of certain families. It seems, therefore, that unrepresented civilian witnesses on the stand represent fair game for the probing broadsides of the soldiers' counsel.
THIS, though, has left the concept of fairness open to question in a few instances. For example, Michael Bridge, one of those wounded on the day, had a previous British court conviction, dating back to 1965, "sprung" on him as he gave evidence. When he queried the relevance of this, he was told that the tribunal might see fit to take significant former convictions into account when assessing the credibility and character of witnesses.
Bridge appeared to raise a legitimate issue of common equity when he pointed out that the paratroopers who carried out the shootings will presumably be spared such ignominy. Since they have been granted strict anonymity, their names cannot be associated with past criminal offences and promulgated on the Internet.
It may even be that specific details of any past convictions cannot be given, as they might be traceable by a search of public records and anonymity thereby compromised.
Neither the tribunal nor its counsel appeared to acknowledge the evident unfairness of this and no counsel rose to support Bridge's point.
The tribunal, it should be noted, is absorbed in a very substantial background legal and political tussle which goes to the nub of its ability to carry out its mandate in a fair and open fashion.
The British Home Secretary and the Defence Secretary are separately seeking Public Interest Immunity (PII) for certain intelligence material, in order to prevent the public disclosure of these documents and their contents.
In some of this material, unnamed agents and informers relay uncorroborated and serious allegations against Martin McGuinness, and reports about paramilitary style "drilling" in the Bogside.
An alleged IRA informer codenamed Infliction is involved, as well as agents who are also identified only by code letters. Aside from the personal allegations against McGuinness, the material could, on the face of it, be significant in the tribunal's eventual assessment of Bloody Sunday.
The dilemma facing the tribunal is that if it refuses to concede the PII application, its decision will almost certainly be subject to judicial review in higher British courts. It could well be overruled, as it was when it initially refused anonymity to soldiers, and it will then have to assess whether it can fulfil its mandate as set out by the British parliament.
Clarke has even postulated a situation where the tribunal, in the worst case scenario, would have to go back to parliament and announce that it can no longer honestly and fairly do the job it was given.
The situation is more complicated because, at this stage, European Human Rights Law can be invoked - especially Article 2 provisions on the right to life - by either or both of the main represented parties: the victims' next-of-kin and the soldiers.
We are set for a fascinating, if intricate, legal debate on what is the nature of "the public interest", who decides what would harm it, which considerations command priority and which should prevail. Meanwhile, the threads have emerged of the case which legal counsel for the military will advance in respect of the paratroopers shooting dead 13 civilians and wounding 14 or 15 others.
Counsel for the soldiers will contend that there are more than 30 "missing casualties" of Bloody Sunday, and that these were gunmen or bombers whose bodies have been spirited away by the IRA and its supporters.
The military side no longer contends directly that any of the civilians shot on the day were actually carrying weapons or engaged in illegal acts, but rather that they must have been in close proximity to others who were.
This represents a major shift from the conclusions of the Widgery Report and from the contents of press releases and political statements issued in Britain and at Stormont in the aftermath of Bloody Sunday.
But lawyers face an uphill task in trying to justify such a shift of ground, and the relatives of the dead and wounded will be far from happy with the indirect exoneration of their loved ones.
One witness put it simply when counsel suggested to him that he could have been mistaken for a gunman or bomber. It might be possible to try to defend one mistake, he remarked, but hardly 28.
It is still an early stage in the convoluted legal and political maze through which the inquiry is trying to pick its way. Yet we have come a long way from the situation that prevailed in the British parliament on April 19th, 1972, when Lord Widgery's flawed and controversial findings were presented and accepted.
In the debate that followed on that occasion, the leader of the opposition, James Callaghan, said: "These tragic events belong in the past. They took place when there was divided responsibility for security and when it is fair to say that very heavy pressure was being brought to bear upon the army commanders to step up their attitude".
He added: "I do not suppose any of us will ever know whether they were acting on their own judgment or whether they yielded to the judgment of others."
It is the crucial task of the present inquiry to confound that latter assessment. Its prospects of so doing are still in the balance and will remain there for at least two more years of hearings and deliberations.
It is just as well that, as Voltaire also observed, "An Act of Parliament is everything to the English: they love law".