Northern Ireland police release Gerry Adams
Police arrested Adams on Wednesday over the murder of McConville, a widowed mother-of-ten, who was killed by members of the Provisional Irish Republican Army who wrongly believed her to be giving information to British forces.
Adams denies any involvement in the killing or being a member of the IRA.
A file will be sent to the province's Public Prosecution Service (PPS), the Police Service of Northern Ireland (PSNI) added.
"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," the PSNI said in a statement on Sunday.
The extended detention of the Irish nationalist leader was threatening to undermine power-sharing in Northern Ireland.
Sinn Fein said detectives questioned Adams about audiotaped interviews by IRA veterans to a Boston College oral history project that made those claims against him.
The decision to release Adams came after police faced a Sunday deadline to charge or release him or seek a judge's permission to extend his detention, a step they took on Friday when an initial deadline was due to expire.
The IRA abducted, killed and secretly buried McConville. It did not admit responsibility until 1999, when the underground organisation defended its action by claiming she had been a British Army spy. McConville's remains were found accidentally in 2003 near a Republic of Ireland beach.
A 2006 investigation by Northern Ireland's police complaints watchdog found no evidence she had been a spy.
Adams' arrest over the killing of McConville is among the most significant developments in Northern Ireland since a 1998 peace deal ended decades of tit-for-tat killings between Irish Catholic nationalists and mostly Protestant pro-British loyalists.
The Sinn Fein leader, who is a member of parliament in the Irish republic, has been dogged throughout his career by accusations from former IRA fighters that he was involved in its campaign of killings, a charge he has repeatedly denied.
Al Jazeera
