The dispute over secret British intelligence material yesterday brought the Bloody Sunday inquiry to the brink of a crucial decision about its ability to complete its work.
After several days of legal argument, the tribunal judges adjourned yesterday to examine highly classified material in respect of which the Home Office and the Ministry of Defence have claimed Public Interest Immunity (PII), which would preclude their public disclosure.
Earlier, the chairman, Lord Saville, had raised the prospect that they might decide they could not conduct an effective inquiry unless this material is made public.
The secret material includes documents relating to the activities and identities of British Security Service agents and informants who allegedly operated in Derry in advance of Bloody Sunday, January 30th, 1972.
Selective portions already revealed to the inquiry contain controversial claims that Mr Martin McGuinness of Sinn Fein told an informant he had fired "the first shot" on Bloody Sunday, and that another agent saw young men "drilling" in the Bogside in the weeks before the killings.
The British Home Secretary and the Defence Secretary have submitted that national security would be damaged and the lives of persons identified put at risk by publication of the secret material. Both propose to provide more detailed justifications to the tribunal members, but only at restricted, in-camera sessions - a proposal to which the tribunal has not yet agreed.
Lawyers for the next-of-kin of Bloody Sunday victims cited international legislation on human rights to back their argument that there should be full disclosure. Article 2 of the European Convention on Human Rights, binding ratifying states to the principle that everyone's right to life shall be protected by law, is central to the case for full and open investigation.
However, the same article is invoked by lawyers for the Home Office and MoD to support their argument that the state has a duty to protect the life of Security Service agents and that the classified material should be withheld.
Several times yesterday, Lord Saville raised the question of what should happen if the tribunal accepts the arguments about national security, but reaches the view that it cannot conduct an effective inquiry if the classified material is not put in the public domain.
Counsel to the tribunal, Mr Christopher Clarke QC, suggested that if the tribunal then ruled, subject to appeal, that the material should be disclosed, "it might be for Parliament to square the circle".
In such a situation, unless the material was produced, there would be no effective official investigation and a breach of Article 2 rights would exist.
The only way in which the matter could be resolved, other than by production of the documents, "would be if Parliament were to determine that the Inquiry should cease . . ." But this, too, could constitute a breach of the UK's treaty obligations.
Earlier, Mr Clarke listed a number of possible options for the inquiry in this situation. He said it might be appropriate for the tribunal to proceed in stages; first to look at the material, then to decide if further information was required as to its significance.
He commented, however, that if the information was seen by the tribunal, it could not - given its duty to seek to discover the truth by all available means - simply ignore it or pretend it had not seen it.
The inquiry will resume on Monday.