At Stormont on Monday, Mark Durkan said that MI5 had "serious questions to answer" in relation to the killing of Kieran Doherty.
Mr Doherty's body was found dumped on the Braehead Road outside Derry on Wednesday night last week. The Real IRA says he had been one of their members and that they'd killed him for involvement in a "cannabis factory" in Donegal.
The Doherty family has denied the allegation and suggested that MI5 had a hand in the events. What gives this suggestion credibility beyond the ranks of conspiracy theorists is that in the weeks leading up to his death, Mr Doherty had repeatedly complained to local media of MI5 harassment. However, the fact that the questions are credible doesn't mean Durkan will get credible answers. Or any answers. MI5 doesn't do answers. Or credibility.
This matters greatly because MI5 is a major player in the north. The scale of its local operation is startling. Just as startling is the fact that it scarcely rated a mention in the debate over the devolution of policing and justice.
The competing rights of Orange bands and nationalist residents were regarded as far more significant. 'Parochial' would be too grand a word for the hugger-mugger negotiations and po-faced pronouncements.
Putting control in the hands of a power-sharing administration would mark the definitive end of 'political policing', we were told.
But under the arrangements accepted at St Andrews, the lead role in political policing is to be taken not by the PSNI, but by MI5. And MI5's discharge of the role won't come under Stormont control. Not that it's presently under Westminster control, either.
Last Friday, one of the most senior judges in Britain, Lord Neuberger, Master of the Rolls, launched a scathing attack on MI5 for conniving in the torture of former Guantanamo detainee Binyam Mohamed and lying about it afterwards to Parliament.
Neuberger suggested that Foreign Secretary David Miliband had been hoodwinked by MI5 into issuing three Public Interest Immunity Certificates falsely claiming that documents relating to the case should be withheld because national security was at stake.
The real reason, Neuberger proposed, was that the documents supported Mr Mohamed's claim that MI5 officers had flown to Pakistan where he was being held by the CIA to put questions to him, even though the agency knew that he had been tortured by the Americans to try to force him to give information - information which he didn't have.
That is, MI5 condoned and took advantage of his torture and then suborned a government minister to issue a fraudulent document to thwart the efforts of the courts to establish whether this had in fact happened. This is the publicly-stated view, not of a bunch of Left-wing libertarians, but of one of Britain's highest judges.
As for its role in Northern Ireland, Annexe E of the St Andrews Agreement says that MI5 will "continue to run directly a small number of agents who are authorised to obtain information in the interests of national security as distinct from countering criminality".
MI5 is thus sanctioned to run informers in paramilitary groups in the North without the authorisation or knowledge of any office or institution here. Back in 2006, during the Westminster debate on the bill enshrining the St Andrews Agreement in law, Mr Durkan moved an amendment to give the Police Ombudsman powers to investigate security operations which would involve MI5 and the PSNI working together.
He was literally laughed at, accused of sulking at having been sidelined when the deal was being done.
Durkan said then: "If we don't act on this then MI5's role will undermine the whole point of Patten, which was to grant some democratic control and scrutiny over security policies . . . a future Minister of Justice would be standing up in the Assembly unable to give the full intelligence picture as he or she wouldn't have any access to that intelligence."
The Mohamed case shows that, when it comes to control and supervision of MI5, Westminster is useless. Under devolution of policing and justice, Stormont will be worse than useless. This helps explain the scale of MI5's operation here.
In the year after St Andrews - 2007 - MI5 established a massive new facility at Holywood, Co Down. At 10,000 square feet plus an underground section, it has a capacity for 400 employees. Its remit isn't confined to the north. Holywood will assume overall control of the agency in the event of the Thames House, London, headquarters being incapacitated by terrorist attack or other emergency. Many might have thought that the area of the UK most affected by political violence over the past generation would hardly be the ideal location for MI5's second biggest and potentially most important facility.
But that consideration will have been far outweighed by the fact that, once devolution is complete, the north, as far as accountability is concerned, will be a limbo-land for spooks to cavort in. Their natural habitat.
So it will be trebles all round at Holywood when the installation of David Ford as an Executive minister is hailed on the UTV News as signalling that local politicians are at last in control of policing and justice. This time, it won't just be Mark Durkan who's being laughed at, but Stormont itself.