Northern Ireland's Sinn Fein party leader Gerry Adams remains in police custody for questioning about the 1972 abduction and murder of a widowed mother of 10.
Police arrested the 65-year-old Adams on Wednesday.
Adams has acknowledged associations with the IRA, but has repeatedly denied any involvement in the Jean McConville case. She was abducted by the Irish Republican Army from her Belfast home and shot to death.
An IRA veteran said Adams was involved in her killing.
Adams described his contact with authorities as voluntary.
Authorities have long sought to query Adams about the death of McConville, who was accused by the IRA of being a spy for the British army. Her body was secretly buried and found decades later in the Republic of Ireland.