Sinn Fein President Gerry Adams was in police custody tonight being questioned by detectives investigating the murder of Belfast mother-of-10 Jean McConville.
Mr Adams, who has vehemently rejected the allegations made by former republican colleagues that he had a role in ordering the notorious IRA killing in 1972, was arrested this evening after voluntarily presenting himself for interview at a police station in Antrim.
No one has ever been charged with the murder. But after years without progress in the criminal investigation there have been a series of arrests in recent weeks.
A veteran republican - 77-year-old Ivor Bell - was charged last month with aiding and abetting the murder. Five other people have been detained and questioned.
The recent police activity has come in the wake of a decision by a court in the United States that compelled a university in Boston to hand over to the Police Service of Northern Ireland (PSNI) recorded interviews with republicans about Mrs McConville's murder.
Boston College interviewed a number of former paramilitaries about the Troubles on the understanding transcripts would not be published until after their deaths - but that undertaking was rendered ineffective when the court last year ordered that tapes that contained claims about the killing be given to detectives.
In the wake of the recent developments in the case, last month Mr Adams, who has always denied membership of the IRA, said he would be available to meet with detectives if they wished to speak with him.
Mr Adams, 65, a former MP for West Belfast and now a representative for Co Louth in the Irish Dail, presented himself at Antrim police station by prior arrangement with officers.
He issued a statement minutes after the PSNI announced an arrest had been made.
"Last month I said that I was available to meet the PSNI about the Jean McConville case," he said.
"While I have concerns about the timing, I am voluntarily meeting with the PSNI this evening.
"As a republican leader I have never shirked my responsibility to build the peace. This includes dealing with the difficult issue of victims and their families. Insofar as it is possible I have worked to bring closure to victims and their families who have contacted me. Even though they may not agree, this includes the family of Jean McConville.
"I believe that the killing of Jean McConville and the secret burial of her body was wrong and a grievous injustice to her and her family.
"Well publicised, malicious allegations have been made against me. I reject these.
"While I have never disassociated myself from the IRA and I never will, I am innocent of any part in the abduction, killing or burial of Mrs McConville."
A PSNI spokesman said: "Detectives from the serious crime branch investigating the abduction and murder of Jean McConville in 1972 have arrested a 65-year-old man in Antrim. The suspect is currently being interviewed by detectives at the serious crime suite in Antrim police station."
Mrs McConville, a 37-year-old widow, was dragged away from her children in her home in the Divis flats, west Belfast, by an IRA gang of up to 12 men and women after being accused of passing information to the British Army in the city.
She was murdered and secretly buried, becoming one of the so-called Disappeared victims of the Troubles.
An investigation later carried out by the Northern Ireland Police Ombudsman rejected the claims that she was an informer.
She was shot in the back of the head and buried 50 miles from her home. Clearly embarrassed by the killing, the IRA did not officially admit responsibility for the murder until 1999 when information was passed to police in the Irish Republic.
It was not until August 2003 that her remains were found on Shelling Hill beach, Co Louth.