Whether he was a freedom fighter or a terrorist, now he's a detainee. Photographer: Kimberly White/Getty Images
Whether he was a freedom fighter or a terrorist, now he's a detainee. Photographer: Kimberly White/Getty Images

Gerry Adams -- member of parliament, president of Sinn Fein, famed shaker of presidential hands and processor of peace -- has been in jail since Wednesday.

Not for the first time, of course. But for a 65-year-old who had left the revolutionary life behind for one of workaday politicking and amiable tweeting, surely an unexpected twist in life's journey.

Adams turned himself in for questioning in connection with a singularly awful episode of Northern Ireland's civil strife. In December 1972, Jean McConville, a widowed mother of 10, was ripped from the arms of her screaming children and dragged out of her home by a dozen members of the Irish Republican Army. She was tortured, shot and secretly buried. Her orphans were scattered to foster homes.

The motivating theory for the abduction -- that McConville had been an informant for British security forces -- was almost certainly false.

The evidence for Adams's alleged involvement in the case hinges on an ill-considered undertaking at Boston College, called the Belfast Project, in which researchers got former paramilitary fighters to describe their transgressions during the Troubles for an oral history, with the assurance that the information would remain secret until their deaths.

It hasn't worked out so well. In 2011, the U.S. Justice Department demanded that the school turn over the transcripts and tapes of some of the interviews on behalf of the U.K. government, which had gotten wind that the archive potentially contained evidence about the McConville murder. The school fought a federal subpoena, although not very hard, and lost. It eventually turned over a handful of interviews that dealt specifically with the crime.

Two former IRA members who were interviewed in the tapes, Brendan Hughes and Dolours Price, have claimed that Adams ordered McConville's murder. (Hughes said so on the tapes, Price in subsequent press interviews.) They are hardly exemplars of objective testament. And both, more relevantly, are dead, meaning their recollections, accurate or otherwise, won't be of evidentiary value in a trial.

So why arrest Adams now? Perhaps the investigators are, as they say, simply following leads on a murder case. And perhaps Sinn Fein officials are engaging in absurd hyperbole (it wouldn't be the first time) when they argue that Adams's arrest was politically motivated, coming as it did a few weeks before elections in which the party is expected to do exceedingly well.

But here's the problem. There's a decent chance, if Adams is charged with murder, that Sinn Fein would withdraw from the power-sharing arrangement that has kept the peace in Northern Ireland, on and off, for 16 years, potentially leading to direct rule from London and a serious risk of instability. If he's set free, on the other hand, he'll merrily return to his constituents claiming exoneration for a crime that has dogged him for years -- and then the questions will start.

Republicans will want to know, for instance, why the police aren't making arrests for atrocities committed by loyalist paramilitaries. And what about abuses by the Royal Ulster Constabulary? And murderous collusion by British intelligence? And where's the justice for victims of Bloody Sunday and the Ballymurphy massacre and the Dublin and Monaghan bombings? And on and on.

Actually, they're already asking those questions. And the Police Service of Northern Ireland, along with the British government more generally, doesn't have very good answers.

That's because Adams's arrest has brought a simmering failure of the peace process to a boil: The two sides have never found a plausible way to deal with crimes committed during the conflict. The Good Friday agreement resulted in the early release of some paramilitary fighters from prison. But it dealt ambiguously with the "on the runs" (former fighters who had fled the province fearing arrest) and others who were suspected of violence but never convicted. Their alleged crimes now fall under a strange patchwork of inquiries and investigative efforts that are uniformly expensive, slow and unsatisfying.

Richard Haass, the former American diplomat, spent six months last year trying to resolve that issue and a few others. He mostly failed. But his proposal for dealing with past crimes -- which would have rationalized the process and offered a framework for future reforms, and which Sinn Fein signed on to -- was on the right track and ought to be revived.

Adams's arrest, however, seems unlikely to improve negotiating relations any time soon. And it just might make them intolerable.

(Timothy Lavin is an editorial board member at Bloomberg View. Follow him on Twitter at @TimothyBLavin.)