Two Northern Bank staff were questioned today about the £26.5 million robbery in Belfast.
Chris Ward, 24, a hostage during the heist last December, was detained in the west of the city.
Police investigating the raid also held a 22-year-old woman who works for the bank in the Belfast area.
The pair were taken for questioning at a serious crime suite in Antrim, where they can be held for 48 hours.
Three men have already been charged by the team of detectives hunting the gang behind the biggest cash theft in British history, one with the robbery itself.
Weeks after the vaults at the Northern's HQ were cleared, Mr Ward relived his ordeal in a television interview.
He said gunmen who took over his home in the Poleglass district warned him that if he did not obey instructions: "You and your family are dead."
The bank official, who has been off work on sick leave since the raid just before Christmas last year, said he was bundled into a car with a gun pointed at his face.
He was driven to the home of supervisor Kevin McMullan in Loughinisland, Co Down, where the pair were ordered to go in to work as normal the following day.
With Mr Ward's family being held captive in Poleglass, Mr McMullan's wife was taken from her home by gang members.
He said later: "Later Kevin was talking to me and I was talking to Kevin about things that they did say about us, that they knew about us.
"You had to act as if nothing was wrong - it was very difficult to do but you knew in the back of your head that you had to do it, that you couldn't tell anybody.
"It was just terrifying... even the fact that they knew I was involved in Celtic (football club), they knew where I lived, they knew my family, they knew my family's names - they knew about my brother and his girlfriend.
"You are walking up the street now and you are wondering 'Is someone watching me?'."
A small amount of cash recovered across the border in Co Cork is believed to have come from the robbery, which was blamed on the IRA.
The bank was forced to issue redesigned banknotes and withdraw the earlier issue to make the robbers' haul worthless.Reuse content