Senior Sinn Fein member Gerry Kelly has been admitted to Antrim police station where Gerry Adams is being questioned over the 1972 murder of Jean McConville.
Mr Kelly arrived at midday, eight hours before the deadline for police to charge or release the Sinn Fein leader after five days in custody.
He is expected to update the media shortly on Mr Adams' status.
Adams attacks reasons for his detention and denies McConville murder
It is claimed IRA volunteers described what happened the night Jean McConville was murdered to Boston College's "Belfast Project".