The release of Sinn Fein's party chief and Louth TD Gerry Adams by the PSNI means the ultimate decision whether to charge the 65-year-old politician with any offence will be made by Northern Ireland's Public Prosecution Service (PPS) at a later date after reviewing evidence presented by police.
Mr Adams has always vehemently denied allegations levelled by former republican colleagues that he ordered the murder of the 37-year-old widow 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 Police Service of Northern Ireland (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 Fein 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 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, a former MP for West Belfast and now an elected representative for Co Louth in the Irish Dail, presented himself for interview by prior arrangement with detectives. Sinn Fein 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 Fein of attempting to blackmail the police over the arrest of Mr Adams.
His comments came after Sinn Fein 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 Fein 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 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 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 Fein 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."
Mr Adams has yet to emerge from Antrim station. A group of loyalists have gathered at the gates waving Union flags.
Earlier, senior Sinn Fein representative Gerry Kelly insisted the party still believed in the PSNI.
After visiting Mr Adams inside the police station, Mr Kelly said: "We are in policing because we believe in the new dispensation of policing.
"If the policing which we see is wrong then we will speak out against that."
Mr Kelly, a North Belfast Assembly member, said his party was "assessing" its position on policing.
"This is quite a serious situation," he said.
"He is leader of Sinn Fein, he is being questioned about things that happened over 42 years ago and let me say this very clearly, the McConville family and the suffering that they have gone through is not going to be assisted by another injustice which is being perpetrated now."
Timeline of events
1972: Mrs McConville is dragged screaming from her home in Divis flats in west Belfast by an IRA gang of around 12 men and women. It is the last time her children see her alive. She is shot in the back of the head and secretly buried, so becoming one of the 'Disappeared' victims of the Troubles. In the 42 years since no one has been charged with her murder.
1999: One year after the signing of the historic Good Friday peace accord in Northern Ireland, the IRA finally admits responsibility for killing the 37-year-old widow, claiming she was an informer for the British Army.
The Independent Commission for the Location of Victims' Remains is set up by the British and Irish governments and the IRA passes on information on Mrs McConville's possible whereabouts on a stretch of coastline in Co Louth. But subsequent searches by the Irish police fail to find her body.
2001: Academics, historians and journalists embark on a five-year project to collate an oral history of the Northern Ireland Troubles. The Boston College initiative involves interviewing former paramilitaries about their roles in the conflict on the understanding their accounts would not be made public until they die.
2003: The body of Mrs McConville is finally found by a dog walker on Shilling beach in Co Louth after a heavy storm exposes her remains.
2006: An investigation by Northern Ireland's then police ombudsman Nuala O'Loan rejects the IRA claim that Mrs McConville was an informer.
2008: Brendan Hughes, a former IRA commander in Belfast who was one of the figures interviewed for the Boston College project, dies.
2010: A book containing excerpts from Hughes's interviews is published. Among claims outlined in Voices from the Grave is the allegation that Gerry Adams ordered the murder of Mrs McConville. Mr Adams emphatically rejects the accusation.
In the same year Dolours Price, who was convicted of the IRA's bombing of the Old Bailey in 1973, makes similar allegations about Mr Adams. Price indicates that she has also spoken to researchers at Boston College.
Mr Adams again denies the claims and highlights both Price and Hughes' criticism of his and Sinn Fein's involvement in the peace process.
2011: The Police Service of Northern Ireland (PSNI) launches a legal bid in the US to try to obtain tapes within the Boston College archive that relate to the murder of Mrs McConville.
2013: Dolours Price dies in her Dublin home of a suspected overdose of prescription drugs.
Later in the year the PSNI wins it lengthy court battle with Boston College and a number of the tapes are handed over.
Veteran republican Ivor Bell, 77, from Ramoan Gardens in west Belfast, is arrested and charged with aiding and abetting the murder of Mrs McConville and IRA membership. His lawyer tells a court that the prosecution case against his client is based on an interview he allegedly gave to the Boston College project. The solicitor insists Bell will fight the charges.
Mr Adams, in response to the renewed focus on the McConville case in the wake of Bell's charges, issues a statement indicating he is willing to speak to the officers investigating the case. He again refutes any suggestion he had anything to do with the crime.
At different junctures through March and April, four women and one man, with ages ranging from 56 to 60, are also arrested and questioned about the murder. All five were subsequently released but police are preparing reports on the four women for the Public Prosecution Service to assess.
Mr Adams, after back and forth contacts between his lawyer and detectives, presents himself at Antrim police station for interview. He is immediately arrested and taken into custody - a move that Sinn Fein brands unnecessary and an example of "political policing".