Sinn Fein leader Gerry Adams is to be released without charge and a file sent to the Public Prosecution Service, the BBC has claimed.
Mr Adams has been questioned at Antrim PSNI station since Wednesday after being arrested in connection with the 1972 murder of mother-of-ten Jean McConville.
The 37-year-old widow was abducted from her home in west Belfast, shot and secretly buried by the IRA.
Her body was found a beach in County Louth in 2003.
Mr Adams has always denied involvement in the killing.