Senior Belfast republican figure Bobby Storey was released on Thursday night following his arrest in connection with the 1972 murder of Jean McConville.
A report is being sent to the North’s Public Prosecution Service.
Mr Storey, who is the Northern Ireland chairman of Sinn Féin, was brought to Antrim police station for questioning about the abduction, interrogation and secret burial of Ms McConville in Co Louth.
He was arrested by detectives from the PSNI’s senior crime branch. Police did not name Mr Storey as the person arrested but well-placed sources confirmed he was taken in for questioning.
Detective Inspector Neill McGuinness said the 58-year-old suspect was arrested as part of the “overall “investigation of the murder of the 37-year-old mother of 10.
Ms McConville was one of the Disappeared, people who were abducted and murdered and secretly buried by republican paramilitaries, mainly by the IRA.
Her body was found on Shelling Hill beach in 2003.
She was a widow and the circumstances and the nature of her killing, which her children abandoned and subsequently taken into care, made her murder one of the most notorious of the Troubles.
The IRA claimed she had been assisting the British army while her family said she was taken away by an IRA gang because she had comforted an injured British soldier shot close to her flat in Divis in west Belfast.
A Police Ombudsman investigation in 2006 found no evidence to support the IRA claim that she allowed the British army place a transmitter in her home.
