Sinn Fein leader Gerry Adams is still being questioned by detectives about the IRA murder of a Belfast mother-of-10 after they were granted more time to quiz him.
Last night a judge allowed the PSNI a further 48 hours to hold the party president at Antrim police station.
Mr Adams, 65, vehemently denies allegations levelled by former republican colleagues that he ordered Jean McConville's murder and secret burial in 1972.
A PSNI spokesman said: "Detectives from Serious Crime Branch investigating the abduction and murder of Jean McConville in 1972 have been granted an extra 48 hours to interview a 65-year-old man who was arrested in connection with the investigation on Wednesday 30th April."
Mr Adams' party colleague and Stormont deputy first minister Martin McGuinness has claimed a "cabal" within the PSNI was behind the arrest, with the intent of damaging the peace process and inflicting political scars on Sinn Fein in the month of an election.
Mr McGuinness indicated that Sinn Fein would review its support for policing in Northern Ireland if Mr Adams is charged by detectives investigating the murder of Mrs McConville.
The deputy first minister said he and colleagues would not be making a "knee-jerk" decision, but suggested they would "reflect" on their endorsement of the PSNI if such a situation came to pass.
Mrs McConville was dragged screaming from her children in the Divis flats in west Belfast by a gang of up to 12 men and women after being wrongly accused of informing to the security forces during the height of the conflict.
She was interrogated, shot in the back of the head and then secretly buried - becoming one of the "Disappeared" victims of the Troubles. Her body was not found until 2003 on a beach in Co Louth, 50 miles from her home.
Mr Adams, a former MP for West Belfast and now an elected representative for Co Louth in the Irish Dail, voluntarily presented himself for interview at Antrim PSNI station by prior arrangement with detectives.
Sinn Fein's decision to sign up to support the police in 2007 was viewed as a major milestone in the peace process and prompted the return to devolved rule at Stormont, with the republican party and the Democratic Unionists entering government together.
The Prime Minister has urged the leaders of Northern Ireland's power-sharing government to co-operate after the arrest prompted sharp divisions between them.
David Cameron spoke to first minister Peter Robinson and Mr McGuinness, who head the devolved administration at Stormont, amid heightened republican anger at the timing of the Mr Adams' detention just before an election.
Mr McGuinness has acknowledged that Mrs McConville was the victim of a terrible wrong done by the IRA but said Wednesday's action was a deliberate attempt to influence the outcome of European elections due in three weeks' time.
DUP leader Mr Robinson said it would have been political policing if the PSNI had decided not to investigate Mr Adams because of the pending poll.
It is the latest dispute which has bedevilled the Stormont regime.
While uniting to condemn violence by dissident republicans opposed to the peace process, many key decisions remain in limbo because of differences between Sinn Fein and the DUP.
At the end of last year, the five main Stormont parties failed to agree on dealing with the legacy of 30 years of violence which has left thousands of victims, controversial Orange Order and republican parades and the display of the British flag on public buildings.
'Review' PSNI support
Mr McGuinness said Sinn Fein would "reflect" and "review" its support for policing in the region if Mr Adams is charged.
But he urged republicans to remain calm if and until that happened.
"We are very thoughtful and we are very reflective but I think if such a scenario does develop then we will sit down and we will reflect on what will be an even more serious situation than the one we face today," he said.
"Obviously in the context of the scenario we find ourselves in at the minute we will have to, on an ongoing basis, monitor this situation where our party leader is being detained and I think you can draw your own conclusions.
"Depending on what happens this scenario will either be resolved in a satisfactory way, in which case we will continue to press on, continue to support the reformers within policing who have made, I think, such a massive contribution to the change of the policing arrangements that we have enjoyed in the course of recent times or the situation will not work out in the way we believe that it should.
"If it doesn't, we will have to review that situation and we will have to review that situation in the context of continuing with our very positive and constructive role within what is a vitally important peace process."
Sinn Fein's decision to sign up to support the police in 2007 is viewed as a major milestone and prompted the return to devolved rule in the region, with the republican party and the Democratic Unionists entering government together.
Withdrawal would be a huge blow to the peace process.
Sinn Fein assembly member Alex Maskey said this morning that the party would "continue to monitor and review our relationship with the PSNI".
He said: "Martin McGuinness actually didn't say that we will withdraw support for policing, we will not withdraw support for policing of course, because we do support policing.
"What we will continue to monitor and review is our relationship with the PSNI if indeed we have a situation which we believe is continuing at the moment, where we have a small element of people involved in policing who are politically motivated, who have a hostile attitude to our party, who have been taking very retrograde steps in relation to how they deal with policing."
He told BBC Radio 4's Today programme: "Police in any part of the world have to earn the respect of their local community. I can tell you that the community that I represent, the people that I represent are scathing in their anger at the moment about the PSNI."
Dolores Kelly, the SDLP's spokesperson on policing, said Mr McGuinness’ threat to withdraw support was "incredibly ill-judged".
"The SDLP fought and won the Patten reforms to ensure that policing was not subject to political interference," she said.
"Sinn Féin belatedly accepted these reforms so it is incredibly ill-judged that Martin McGuinness would now make such comments which are clearly in contravention of both the word and the spirit of the Patten reforms. It is very far from where, in the assessment of the SDLP, either nationalists or unionists are.
She added: "For Sinn Féin to threaten to withdraw support from the PSNI because an investigation is not going the way they want it completely unacceptable... For anyone, or any party to try to unpick the progress we have made is just wrong. Sinn Féin must realise that these threats are very damaging."
"No dark forces"
Meanwhile, Northern Ireland's justice minister has said he can see no sign of dark forces operating within the police service.
Martin McGuinness on Thursday criticised some elements within the Police Service of Northern Ireland for detaining Gerry Adams three weeks before the European elections.
Stormont Justice Minister David Ford said: "If there are dark forces within policing, I can see no sign of dark forces.
"I see a police force with very high levels of confidence, higher than the Garda Siochana (Irish police) or many forces in Great Britain, and I see a police force carrying out its duties properly and appropriately, following up evidential opportunities where they present themselves and operating in conjunction with the community across a range of issues."