Pinning IRA membership on the Sinn Fein president, Gerry Adams, has proven just as difficult over four decades as finding the missing Malaysian airliner in the past month in the Indian Ocean.
I recall being at Crumlin Road courthouse in 1978 when the then Lord Chief Justice, Sir Robert Lowry, said there was insufficient evidence to convict Adams of membership. He was carried out through the courthouse gates on the shoulders of his cheering supporters.
I recall, too, interviewing Adams on many occasions, when he was regarded generally by the media as the kingpin IRA strategist.
However, if I were asked to testify today as to whether he ever betrayed that he was directing any IRA operations, I would have to say that not once did he do so in any of those encounters.
No one had any doubt that he was the chief mouthpiece of the republican movement.
If he had not been, why would he have been flown secretly from his internment in Long Kesh, along with Martin McGuinness, then an IRA leader in the Bogside, for talks with the first Secretary of State for Northern Ireland, William Whitelaw, in a swish corner of Chelsea?
Adams's reputation went before him in the eyes of the hundreds of foreign journalists who flocked to Belfast in the 1970s. However, he was very careful to avoid incriminating himself.
In all my personal contacts with him, he never confessed to direct IRA membership and he would preface and qualify his views with phrases such as "While I don't speak for the IRA..."
As time passes, the IRA's omerta code of silence is clearly not as watertight as it once was.
Martin McGuinness is on record as saying he would die rather than break his vow of secrecy, but the stresses and strains between the peace process republicans and dissidents are leading to more revelations, true or false, about the past.
A succession of barbarous tales of terrorism is now emerging, of which the terrible fate of Jean McConville is but one of many grotesque chapters.
The Sinn Fein leadership appears powerless to stop the revelations and cannot be certain as to where they will eventually lead.
Nearly two decades after the Belfast Agreement, the party still clings to its paramilitary roots, as evidenced by the influence of so many ex-IRA figures in its upper ranks.
Perhaps a turning-point is being reached for Sinn Fein, particularly in the south, with the linking of Adams (right) to such a heinous crime as the McConville murder.
In the judgment of respected Dublin commentators, Sinn Fein has made a wrong call in blaming his arrest on "dark forces" within the PSNI.
How will Adams's detention in Antrim play out in the forthcoming election?
Could it be that younger voters, in particular, are in no mood to be reminded of the Troubles as the southern economy climbs out of recession?
To what extent is support for Sinn Fein a protest against the Republic's established parties upon whom the blame has fallen for the country's economic woes?
Up north, the arrest of Adams should help restore confidence, especially amongst the unionist community, that the rule of law is being even-handedly applied after the on-the-run debacle.
Only last week, the PSNI was roundly attacked by a High Court judge for its handling of loyalist parades and the First Minister, Peter Robinson, said he believed "certain people" – presumed to be senior republicans – were being "left alone".
Mr Robinson told the Assembly: "I have consistently indicated that I believe certain people have been left alone, because of their involvement with the political process which the Government do not want to disturb."
The comments of Mr Justice Treacy in the High Court are damaging for the PSNI's reputation and well might the Chief Constable Matt Baggott seek redress.
To be accused by the judge of "unjustified enforcement inertia" and of failing to prosecute "proactively, or at all" those involved in illegal parades, is a fairly damning indictment of Mr Baggott's police force.
Broadly speaking, the police have built and retain respect across a wide cross-section of this society – unionist, nationalist, Protestant and Catholic alike.
It is essential that the PSNI demonstrates total independence, but that is exceedingly difficult where so much power and influence is now vested in local politicians in such a divided society.The stability of Northern Ireland will not be helped if the PSNI is treated as a community football to be kicked about as politicians please.