The couple arrested in a sizeable police operation in south Armagh on Tuesday were still being questioned last night about the Omagh atrocity.
They had their detention extended by a further 72 hours. A decision to release or charge them will have to be made inside that time.
The husband and wife were in custody at Gough Barracks in Armagh city and have been questioned about the Omagh bombing of August 1998 and other paramilitary crimes by anti-agreement dissidents.
These are understood to include other town-centre bombing incidents in Lisburn, Co Antrim; and Moira and Banbridge in Co Down.
The pair were arrested at dawn on Tuesday at an address in Jonesborough.
Some 200 police with British army support were involved.
The man has been questioned before about the bombing - the single worst atrocity of the Troubles in which 29 people died, including the mother of unborn twins.
Families of the Omagh dead and maimed remain cautiously hopeful of a breakthrough in the case. Senior security sources have confirmed the arrests represented a significant breakthrough in the five-year hunt.
Nobody has yet been charged in direct connection with the bombing. Michael McKevitt, the alleged "Real IRA" leader at the time of the atrocity, was jailed for 20 years last month for the new crime of directing terrorism - the first to be convicted. Colm Murphy, another Dundalk man, has been sentenced to 14 years for conspiring to cause an explosion.
Omagh relatives will meet the Minister for Justice, Mr McDowell, in Dublin on Monday to seek his agreement that Garda experts can give evidence in a Belfast High Court civil action taken by them in which McKevitt, Murphy and three others have been named.