Even if further prosecutions were to emerge from these latest police inquiries into Captain Robert Nairac's murder, the convicted killers would not have to serve a day's sentence in prison.

That is because under the 1998 Good Friday agreement a form of amnesty was granted to those who committed so-called scheduled offences, otherwise known as terrorist or political crimes, depending on one's point of view.

Hundreds of convicted terrorists were released from prison after the agreement was signed. In these circumstances a valid question arises over the cost in police and legal time in pursuing prosecutions against Nairac's alleged killers.

Northern Ireland's past has been described as an industry in some quarters — including government sources, in private — with lawyers the chief beneficiaries.

The cost of the Bloody Sunday inquiry, which was established to re-examine the deaths of 13 demonstrators during an illegal civil rights march in Londonderry in 1971, has passed £181million. More than three years after the last witness gave evidence, there is no sign that publication of its report by the inquiry chairman Lord Saville of Newdigate is imminent.

Martin McGuinness, the Northern Ireland Deputy First Minister who admitted he was an IRA commander on Bloody Sunday, confirmed recently that he told Jonathan Powell, Tony Blair's adviser on the peace process, that the inquiry was unnecessary and that a government apology would have been sufficient.

Three other inquiries into the controversial killings of Robert Hamill, Rosemary Nelson and Billy Wright — which were agreed as part of political negotiations in the wake of the Good Friday agreement — have already cost tens of millions of pounds.

The family of Pat Finucane, a solicitor murdered by loyalist terrorists, and relatives of victims of the 1998 Omagh bombing are also demanding independent public inquiries.

Every now and then Northern Ireland is doomed to be haunted by its past deeds. It is for this reason — and the panic engendered in government circles by the seemingly endless cycle of inquiries — that the Consultative Group on the Past was established, with a remit to suggest a solution to the legacy of violence.

The group, headed by Lord Eames, the former Church of Ireland Primate, and Denis Bradley, a former Catholic priest, is due to issue its report this summer.

Experience would tend to suggest that the pessimists will be proven right and that they will not find a route out of the past that will satisfy everybody. The Government would probably agree to anything that guaranteed an end to the dizzying costs of inquiries.

31-year inquiry

— May 14-15, 1977: Captain Robert Nairac is abducted, tortured and shot by IRA operatives

— 1977: Liam Townson is found guilty of murder and given a life sentence. He was released in 1990

— 1978: Five more men are convicted in connection with the case, two of murder. Three other suspects remain on the run

— 2007: One of the fugitives, Terry McCormick, who lives in the US, appears in a television documentary giving new information about the murder

— May 20, 2008: A man is arrested in Jonesboro, South Armagh, in connection with Nairac's death

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