SINN Fein leader Gerry Adams remained in police custody last night as the fallout over his dramatic arrest drove a deep rift through the heart of Government in Northern Ireland.
The contentious Boston College tapes and claims from former republican allies are understood to have led to Mr Adams' arrest in connection with the murder of mother-of-10 Jean McConville.
Sinn Fein reacted with fury to the detention of its president, with Martin McGuinness blaming the "dark side" of policing conspiring with enemies of the peace process.
Mr Adams will be quizzed again by detectives today. The 65-year-old was arrested under the Terrorism Act at Antrim Serious Crime Suite by police investigating the 1972 murder of Mrs McConville.
He strongly denies any involvement in the killing and disappearance of the 37-year-old widow.
He was detained after voluntarily attending for questioning with his solicitor on Wednesday evening.
Mr Adams is being questioned largely regarding claims made in the so-called Boston tapes, although police sources told this newspaper the arrest followed additional intelligence being brought to the attention of the PSNI.
Deputy First Minister Mr McGuinness said the questioning centred on books Mr Adams had written and what others said about him – those "maliciously and vehemently" hostile to the peace process.
It is believed a number of recent newspaper reports were presented to Mr Adams during his questioning. Investigators initially had 24 hours to quiz him regarding Mrs McConville's disappearance. At 8pm last night a senior police officer gave permission for an additional 24 hours of questioning.
Currently, police can detain Mr Adams until 8pm this evening. Should they wish to seek further time they must apply to a court judge.
The political fallout from Mr Adams' arrest raged throughout yesterday, with Sinn Fein accusing the PSNI of political policing and questioning the timing of the arrest, three weeks before the European and council elections.
One of Mrs McConville's children, Michael, said he feared giving police the identities of those who killed his mother, as he feared for his life.
He said he wanted the perpetrators to be tried as "war criminals" at the international court in The Hague, rather than being brought before courts here.
First Minister Peter Robinson praised police for the latest move.
"It strengthens our political process in Northern Ireland for people to know that no one is above the law, everyone is equal under the law, and everyone is equally subject to the law."
However, Mr McGuinness blamed the "dark side" of policing for his leader's detention during an election campaign and insisted Mr Adams could have been questioned without being arrested.
Asked about claims the arrest was politically motivated, Prime Minister David Cameron said: "There has been absolutely no political interference in this issue."
A veteran republican – 77-year-old Ivor Bell – was charged in March with aiding and abetting the murder. He denies the claims. Five other people have been detained and questioned.
Mrs McConville was dragged from her home in 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.
She was murdered and secretly buried, becoming one of the so-called Disappeared. An investigation later carried out by the 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 gardai.
It was not until August 2003 that her remains were found on Shelling Hill beach, Co Louth.
Chief Constable Matt Baggott defended his officers at the Policing Board.
"Effective investigation applies to any unsolved matter and it would be inappropriate for me to comment on any individual investigation other than to say they will be objective and methodical," he said.
McGuinness: It's the dark side of policing with clear political motive
THE Deputy First Minister has blamed the "dark side" of policing conspiring with enemies of the peace process for the arrest of Gerry Adams.
Martin McGuinness acknowledged that Jean McConville was the victim of a terrible wrong done by the IRA, but said Wednesday's detention was a deliberate attempt to influence the outcome of European elections due in three weeks' time.
The head of Sinn Fein's team at Stormont has strongly condemned the shooting dead of police officers by dissident republicans opposed to the peace process.
But the arrest of Mr Adams in the midst of an election campaign has angered republicans who hope to make major vote gains in the South.
Mr McGuinness said: "I think we have seen that dark side flex its muscles in the last couple of days."
Mr McGuinness said serious questions had to be asked about the agenda of those behind the arrest.
"In the mouth of an election the leader of a political party experiencing huge growth all around the island finds himself under arrest," he said.
He claimed Sinn Fein had been told by "senior" and "reforming" figures within the PSNI that there was still a dark side within policing.
He said some former republicans who were "maliciously and vehemently" hostile to the peace process had been targeting Mr Adams.
"It is quite disappointing to see the efforts of those people now in consort with the dark side within policing," he added.
Mr McGuinness said his colleague played a pivotal role in bringing peace.
"For over 20 years we have worked very, very closely in developing the peace process, bringing about the political and security transformation that the public enjoy today and, in my opinion, in the course of supporting the peace process, he has been the single most influential figure in the process," he said of Mr Adams' role.
Robinson: It is proof of force's impartiality. No one is above law
PETER Robinson said the arrest of Gerry Adams was proof of the police's impartiality and a healthy political development.
He said yesterday: "Is anybody going to say to me that if the police are aware of claims and evidence in relation to such a barbaric killing, that it would be political policing for them to question those who have been suggested to have been involved?
"I would suggest to you that it would be political policing if the PSNI had not questioned those that were deemed to have been involved in any way.
"I cannot say whether Mr Adams will be charged or released, whether he will be held for a further period, whether even if charged he might be convicted.
"But what I can say is that it strengthens our political process in Northern Ireland for people to know that no one is above the law – everyone is equal under the law and everyone is equally subject to the law."
The First Minister went on to deal with the perceived threat to Jean McConville's son Michael.
He said: "We have had a lot of words from Sinn Fein about how wrong what happened to Mrs McConville was.
"Here is an opportunity. This is the same republican movement of which they are a part, that the people who carried out this act were a part. Let them meet Michael McConville, let Michael McConville impart to them the names of those who were involved.
"I challenge Sinn Fein that they should do their civic duty and responsibility of handing over those names to the PSNI."
Ulster Unionist Party leader Mike Nesbitt said: "It is, quite frankly, outrageous for Martin McGuinness to blame what he calls 'the dark side of policing in Northern Ireland' for the arrest.
"Quite simply, the police must be allowed to follow evidence wherever it leads them.
"It is a fundamental legal principle that justice and the due process of law must apply equally to everyone in a society."