Months of delicate negotiations will follow yesterday's ground-breaking development in which Mr Martin McGuinness of Sinn Fein finally supplied the Saville Tribunal with an account of his own and the IRA's role on Bloody Sunday.
Tribunal lawyers promptly set out to try to arrange a personal meeting with Mr McGuinness, who is believed to have confirmed in his draft statement that he was a member of the IRA's Derry brigade command staff and actually issued the operational orders for the day.
The far-reaching significance of this clear signal that the republican movement has decided to co-operate with - and therefore extend ad hoc recognition to - a Crown institution cannot be overestimated.
But it is reliably believed that Mr McGuinness, with the active support of his lawyers, will resolutely resist attempts which inevitably will be made to extend his testimony beyond the actual events of Bloody Sunday.
He will, for example, refuse to give the names of IRA colleagues or to be drawn on details of IRA operations before and after Bloody Sunday. The tribunal chairman, Lord Mark Saville, and his fellow judges may have to draw a fine line between questioning which tests Mr McGuinness's evidence and that which could amount to an open-ended trawl through the IRA's operational secrets.
Relatives of Bloody Sunday victims welcomed yesterday's breakthrough and a spokesman urged all others to follow Mr McGuinness's example. While the North's Education Minister may have set something of a moral pointer, however, there is unlikely to be a rush of former Provisional IRA members offering themselves to the inquiry.
While Mr McGuinness's decision will not have been reached without intense background discussions with republican colleagues and careful legal advice, it is thought certain that the option to come forward and cooperate with the inquiry, or not, will have been left to the individual decision of other IRA activists of the time.
Mr McGuinness, who was Sinn Fein's chief negotiator on the Belfast Agreement talks, has come under intense pressure in recent months, inside and outside the inquiry, to co-operate with the new search for the truth behind the killings on January 30th, 1972.
He may feel compelled to seek to refute directly the allegations made against him in documents partially revealed to the inquiry by the British Secret Service. In this material, an unnamed agent claims to have been told by an informer that Mr McGuinness had privately admitted firing "the first shot" on Bloody Sunday.
In his draft statement, faxed to the tribunal yesterday by his Belfast solicitor, Mr Barra McGrory, Mr McGuinness strongly denies this charge. He says that no Provisional IRA members opened fire at soldiers on the day (several former Official IRA members will admit to firing shots) and that he himself was with the civil rights march from beginning to end.
He asserts that, on his instructions, only two Provisional IRA armed units - each consisting of four men - were kept on standby in the Creggan and Brandywell areas, and that all other weapons were secured in dumps.
It is certain that the tribunal, and counsel for the soldiers, will press strongly that these key individuals, at the very least, should be identified and that those among them who survive should give evidence.
Mr McGuinness said in Belfast yesterday that it would not be appropriate for him to discuss the content of his statement in any way. He indicated that he had reached his decision to testify because he intended "standing with the people of Derry in their quest for justice and truth".
The tribunal's solicitors will need to meet Mr McGuinness, according to sources, to take a formal statement, which may be largely based on his draft submission but which they may also seek to expand. When a full statement is agreed upon by all sides and is formally signed by Mr McGuinness, the tribunal will rule upon his lawyer's request that he be granted full legal representation at the hearings. After that a date will be set for his evidence, but considering the delicacy of the negotiations and contacts which must first take place, that is likely to be several months away.
In the meantime, the tribunal has yet to rule on applications by British ministers for Public Interest Immunity (PII) in respect of the secret material which contains the allegations against Mr McGuinness.
They are, in effect, claiming privilege in respect of all this material and the names of the agents and informers involved in creating it.
No matter what the tribunal rules on this, higher courts may be drawn in by way of applications for judicial review of the ruling and delays may ensue.
Equally, if Mr McGuinness is given any concessions by way of delimiting the areas upon which he can be questioned by counsel at the inquiry, this also may be subject to a judicial review application by lawyers for the soldiers.