It seems probable that the Taoiseach is right in saying that the Minister for Justice would not be obliged to release Garda McCabe's killers prematurely: explaining why takes rather longer and has to be rather more qualified than the Taoiseach's crisp statement.

Leaving public outrage, morality, the need to protect the community, the desire to placate Sinn Fein or the IRA and all other extra-legal considerations aside and focusing exclusively on the legal factors, this question depends upon the Criminal Justice (Release of Prisoners) Act, 1998.

The question turns upon the Act rather than the agreement reached in the multi-party talks in Belfast because it is the Act which constitutes the law here (though this does not make much difference since the relevant part of the agreement is scheduled to the Act and amplified in it).

The system set up by the Act is fairly straightforward. The decision on early releases is left, ultimately, in the hands of the Minister for Justice. But he is subject to three conditions. In the first place, the prisoners must be "affiliated" to an organisation which "has established and is maintaining a complete and unequivocal ceasefire . . . The situation in this regard will be kept under review."

What this plainly means is that the Minister may only consider releasing the prisoners if he believes the IRA continues to meet this commitment. Obviously, though, there would be political pressure on the Minister not to reject a claim for release on this ground because of the Government's perceived need not to admit that there had been a breach in the ceasefire. Secondly, there is an advisory body, the Release of Prisoners Commission, shared by a senior counsel and with two other members, a civil servant from the Department of Justice and a member of the Probation and Welfare Service. But the commission's power only extends to giving what is, as the Act says, "advice". Analogous arrangements exist elsewhere. Take, for example, the situation where a person is found not guilty of murder by virtue of insanity and is detained until he is well enough to be released.

This is obviously a sensitive decision, not least because the community into which he will be released will usually include the family of his victim. Accordingly, a commission has been set up to advise on this decision too. In Re Gallagher's Application 1996 it was held, reasonably enough, that the Minister was not obliged to follow the commission's advice to release. I should expect the same decision in parallel circumstances involving advice from the Release of Prisoners Commission. The third and most crucial point concerns the guidelines the Minister and the commission must follow in regard to releases. The only published guidelines are those set out in the Belfast Agreement and repeated in the Act.

According to these: "The review process would provide for the advance of the release dates of qualifying prisoners while allowing account to be taken of the seriousness of the offences . . . and the need to protect the community. In addition, the intention would be that, should the circumstances allow it, any qualifying prisoners who remained in custody two years after the commencement of the scheme would be released."

Let us consider what might happen if releases were refused, say in the year 2000, and the disappointed prisoners brought a case against the Minister by way of judicial review. The court's interpretation of the words just quoted would probably be crucial. Plainly, the final sentiment is the one on which people who support early release would fasten. However, it seems to me that the words "the intention . . . should the circumstances allow it" indicate that this is an aspiration rather than a binding commitment.

Moreover, the second sentence has to be balanced against the earlier one, and as regards this, the offences could hardly be more serious, involving the most heinous end of the manslaughter range and with the victim being a garda, one of the force which must defend society against violent criminals. Finally, "the need to protect the community" is relevant to a particular aspect of last week's trial. This is the intimidation of witnesses, which some people regard as the worst feature of the case. If this organisation, despite the ceasefire, is still capable of this sort of action, surely the community needs protection from it and its agents? There is another range of reasons I think the chance of such a judicial review application succeeding is small. This is that the circumstances are such that any court would go a long way to avoid second-guessing the responsible minister.

First, the courts will usually allow a substantial margin of error in regard to powers of pardon or remission because these only come into play after a person has received a full and fair trial, proof beyond reasonable doubt, and an appeal. Secondly, here the motivation for early release is not even the usual one, depending on individual circumstances, such as fresh evidence of innocence, good behaviour in prisons or a terminal illness. Rather it is an initiative to assist the peace process in Northern Ireland; in other words a highly political matter about the ramifications of which a court is neither informed as to the facts nor qualified to judge. In these unusual circumstances no one could complain if such political factors are taken into account because the whole basis of the concession is a political settlement.

One should add that if any minister were to go the other way - to release the killers prematurely - an attempt might again be made by way of judicial review but this time by, say, the members of the community to which the killers would be returned, to invalidate this decision. But it seems likely that because of the tolerance allowed by the courts to the decision of the minister such an action would also fail. Finally, one ought to make three points of qualification. First, the Minister for Justice's decision will have to be taken by reference to contemporary circumstances at the time when release is considered rather than public outrage at the present time.

Secondly, the Minister cannot behave arbitrarily. He could not, for instance, make a distinction between the killers of a garda and of an RUC officer, releasing the latter but not the former. In the context of a Northern Ireland settlement that would probably be regarded as arbitrary (despite the fact that this distinction disfigured the law on the non-extradition of so-called "political offenders" in the 1980s).

Thirdly, from a legal perspective - whatever about the political difficulties - it behoves politicians not to try to commit themselves now as to what will happen in the future, when the discretion is actually exercised. All in all, it seems that provided any refusal follows a fair procedure and is not unreasonable or discriminatory, the courts would not interfere with the decision of the Minister for Justice who has been appointed to deal with the matter by the elected government.

This is something it would be well to bear in mind in case, some time down the road, if a future minister seeks to release the killers of Garda McCabe while offering legal considerations ("the advice of the Attorney General") as a fig leaf for doing that which he wants to do anyway for political reasons.

David Gwynn Morgan is professor of law at UCC