Gerry Adams has been released from custody this evening and a file is to be sent to Northern Ireland's Public Prosecution Service.
The file will decide whether there is a case to answer.
The Sinn Féin leader had been held by the PSNI at the serious crime suite in Antrim since Wednesday evening.
Deputy Adams was being questioned in relation to the disappearance and death of Belfast mother of ten Jean Mc Conville in 1972.
A PSNI spokesman said: "A 65 year old man arrested by detectives from PSNI's Serious Crime Branch investigating the abduction and murder of Jean McConville in 1972 on Wednesday 30th April has been released pending a report to the PPS.''
While a decision on whether to proceed with a prosecution of Mr Adams would ordinarily rest with the region’s Director of Public Prosecutions Barra McGrory QC, it is likely that he will delegate the case to another senior PPS official, as he has previously acted as Mr Adams’s lawyer prior to becoming DPP.
It could take some time for the PSNI to prepare the file for the PPS, with prosecutors then taking a further period to assess whatever evidence is presented.
The announcement of Mr Adams’ release came almost 96 hours after the republican veteran was arrested on Wednesday night after voluntarily presenting himself at Antrim police station for questioning.
His detention has triggered a major row at the heart of Northern Ireland’s powersharing institutions, with Sinn Féin accusing an anti-peace process “rump” within the PSNI of orchestrating the arrest, branding it an example of “political policing” specifically timed to damage the party’s chances in the forthcoming European and local government elections.
Those claims have been emphatically rejected by British Prime Minister David Cameron, Stormont First Minister Peter Robinson and Justice Minister David Ford.
Mrs McConville was dragged, screaming, away 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.
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 presented himself for interview by prior arrangement with detectives. Sinn Féin has claimed he was not expecting to be formally arrested at that point.
He was questioned for two days before the police successfully applied to a judge in Belfast on Friday for a 48-hour extension to his detention period. It is understood he has been quizzed for up to 17 hours a day.
As the second 48-hour deadline approached, the PSNI announced that he was to be freed pending a report being prepared for the PPS.
Earlier, Democratic Unionist leader Mr Robinson accused Sinn Féin of attempting to blackmail the police over the arrest of Mr Adams.
His comments came after Sinn Féin Deputy First Minister Martin McGuinness suggested his party would review their support for policing if Mr Adams is charged.
Mr McGuinness made the claim in a press conference on Friday, though he did not repeat the assertion as he unveiled a new mural to his party leader in west Belfast yesterday.
Mr Robinson said today: “The publicly conveyed threat to the PSNI delivered by the highest levels of Sinn Féin that they will reassess their attitude to policing if Gerry Adams is charged is a despicable, thuggish attempt to blackmail the PSNI.
“The threat now means that ordinary decent citizens will conclude that the PSNI and the PPS (Public Prosecution Service) have succumbed to a crude and overt political threat if Adams is not charged.”
Sinn Féin’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 DUP entering government together.
First Minister Mr Robinson said: “The PSNI must not be the subject of republican bullyboy tactics. They must be completely free to follow any and all evidence regardless of where it takes them and to decide free of political considerations whether suspects will be charged or not.
“The hive of activity to pressurise the police from charging Adams is obscene politicising of the policing process.
“I warn Sinn Féin that they have crossed the line and should immediately cease this destructive behaviour.”
He claimed the republican movement had shown a lack of leadership.
“Their actions allow only one conclusion to be reached – republicans believe they are not subject to the rule of law in the same way as they demand others to be made amenable to the rule of law.”