Northern Ireland police released Sinn Fein leader Gerry Adams on Sunday and sent a file to the public prosecutor after four days of questioning over his role in a 1972 murder in a case that has rocked the British province.
Police arrested Adams on Wednesday over the abduction and murder of Jean McConville, a killing he said he was "innocent of any part" in. His detention has raised tensions among Northern Ireland's power-sharing government and its fragile peace.
"A 65-year-old man arrested by detectives investigating the abduction and murder of Jean McConville in 1972 on Wednesday 30th April has been released pending a report to the PPS (Public Prosecution Service)," police said in a statement.
Adams' arrest over the killing of McConville is among the most significant 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.
Northern Ireland's Director of Public Prosecutions will now review the police report. The head of the prosecution service, Barra McGrory, is a former solicitor for Adams, a spokesperson for the PPS was quoted as telling Irish media last year.
The PPS was not immediately available to comment. Under the 1998 Good Friday agreement, which drew a line under 30 years of sectarian strife in the British province, those convicted of paramilitary murders during the conflict would have life sentences reduced to two years.