Police have been given another three days to question a man, understood to be Northern Bank employee Chris Ward.
Chris Ward was interviewed on BBC's Spotlight programme
Mr Ward, 24, was arrested on Tuesday by detectives investigating last year's £26.5m robbery at the bank in Belfast.
A 22-year-old woman who was also arrested was released without charge on Wednesday. Both people were arrested at different addresses.
After the robbery, Mr Ward described on television how he was held captive in the run-up to the raid.
The details were given in an interview with the BBC's Spotlight programme.
Mr Ward described how he and a male colleague were forced to facilitate the theft of millions of pounds from the cash centre of the Northern Bank's headquarters.
Police Land Rovers arrived at the Ward family home in the Poleglass area of west Belfast at about 0600 GMT on Tuesday.
PSNI Land Rovers outside the Ward family home
Earlier this month, police investigating the robbery arrested several people.
Of the 10 people questioned to date in connection with the robbery, three have already appeared in court.
The robbery happened at the bank's Northern Ireland headquarters at Donegall Square West just before Christmas last year.
Some money seized in County Cork last February was linked to the robbery, but virtually all of the missing millions remain unrecovered.
Chief Constable Sir Hugh Orde subsequently blamed the IRA for the raid.