A man is still being questioned in connection with the fatal shootings of Brian Downes and Eddie Ward in Walkinstown last month.
A woman was earlier released from custody.
24-year-old Eddie Ward and 40-year-old Brian Downes were both shot dead in an attack linked to organised crime at a garage on the Greenhills Road in Walkinstown, Dublin 12 on 5 October.
The gunman escaped on a motorbike which was later recovered from the Grand Canal near Bluebell in Dublin.
Earlier this month two men in their 20s were arrested.
They were later released without charge.
