Raiders stole £1.2 million from a security van in a kidnap robbery in Belfast yesterday.
One woman was taken hostage by the gang and held for up to eight hours until her partner, who works for Brinks security company, delivered the cash to the waiting robbers at a garage and filling station in the Finaghy area of south Belfast.
The PSNI was last night resolutely refusing to suggest who might have been responsible and would not be drawn on the question of possible paramilitary involvement.
One source said: "We are still at a very early stage in this investigation. Unfortunately there are a number of criminal gangs with the capacity to commit this kind of robbery."
There is not thought to be any direct link to similar robberies carried out in Dublin in recent months or to the robberies last year in Belfast at the Northern Bank and Makro cash and carry which have been blamed on the IRA.
There have been more than 40 robberies involving the taking of hostages in the North in the past two years.
A security source suggested to The Irish Times that copycat tactics were being employed by criminal gangs throughout Britain and Ireland.
Intelligence officers were last night trying to identify those responsible.
The gang responsible began the robbery late on Monday night when they arrived at the couple's home in the Belvoir area of Belfast, not far from the robbery scene.
The Brinks employee was told to meet other gang members at Creighton's Garage, a well-known business not far from the King's Hall in south Belfast.
It is understood he was given specific instructions how to hand over the cash.
"He was to hand over a large sum of cash to an unknown party," a police spokeswoman said.
"Once this handover had taken place the woman was released unharmed in the Annadale area of south Belfast."
The filling station where the handover took place was sealed off for much of yesterday.
A derelict house in Annadale, believed to be where the woman was held captive, has also been searched.
Three other armed robberies were carried out in the greater Belfast area yesterday morning.