A man was being questioned tonight by detectives hunting the bank robbers who carried out a £200,000 (€168,352) hostage raid in Belfast.
He was arrested during searches in the north of the city near where the heist was carried out on Friday.
Thieves ordered an employee to fill a bag with cash from the Ulster Bank branch at Carlisle Circus while they held his partner and one-year-old baby captive at their home.
They were only released when the staff member went into work and stuffed a rucksack with bank notes before taking it to a drop off point in nearby Henry Place.
The victim had been woken hours earlier by three men at his home in Alliance Avenue.
A hood was placed over his head and he was given the bag with which he was to remove money from the bank.
His partner was tied up and their young child held at their home during the ordeal.
Although the raid bore parallels with the £26.5m (€22.3m) Northern Bank robbery in December 2004, which was widely blamed on the IRA, police have so far refused to suggest any paramilitary involvement in the crime.
But after searches today, a police spokeswoman confirmed that one man was helping detectives with their inquiries into the Ulster Bank robbery.
A number of other items were also seized for examination.