The FBI and Police Service of Northern Ireland (PSNI) are working together on what senior officers suspect might be another IRA arms smuggling operation based in Florida.
The case began last November when a Belfast man was found to be attempting to buy large quantities of handguns.
The 58-year-old man, whose wife was killed by loyalists in the early 1970s, is in a Florida prison having pleaded guilty in January to making false statements to acquire guns. He is due for sentence at the end of this month.
An FBI officer involved in breaking up the 1999 IRA gun-running operation in Florida told the Daily Telegraph newspaper last week this case bears resemblances to that operation.
The suspect, Mr Bernard Meli, from west Belfast spoke to a number of arms dealers about acquiring large numbers of weapons, particularly handguns. One source said he was attempting to buy between 200 and 300.
Interviewed in the Daily Telegraph, FBI special agent Mark Hastbacka described Mr Meli as a "little unassuming man" who was not co-operating with the authorities. "He's not very co-operative at all. He's a stand-up guy going down without saying a word." It is believed Mr Meli lived in England for a number of years and worked in the car trade. His wife Sandra was shot dead by the Ulster Defence Association at their home in east Belfast in 1972.
Mr Meli was arrested by the Miami Joint Terrorist Task Force last November after buying a .38 revolver and arranging to buy another 20 guns. He gave a false address to the gun dealer.
Mr Hastbacka was involved in the case in which Conor Claxton, Anthony Smyth and Martin Mullen were sentenced to between three and five years for arms smuggling. Claxton had no known IRA connections and Smyth was thought to have severed links with the organisation many years previously. Mullen was a Sinn Féin electoral worker but with no known IRA connections.
In the previous arms smuggling operation in Florida the IRA acquired several hundred guns, including handguns and automatic shotguns, and sent them by mail to the Republic. Most of the weapons were sent to rented houses where they were collected and distributed to IRA units in the Republic and Northern Ireland.
According to some senior Garda sources, the IRA appears to be replacing the arsenal which it acquired from Col Gadafy's regime in Libya in the mid-1980s. A tranche of these weapons has been destroyed in decommissioning. It is believed the IRA had around 1,000 AK47 assault rifles in its old arms dumps.
It is expected that more of this old arsenal might be destroyed before the general election, if agreement can be reached with the British government over the repatriation of IRA members "on the run" outside the UK jurisdiction.
Police and republican sources reported during 1999 that the IRA leadership was telling its members it would only consider decommissioning as long as it could replace the arsenal with new weapons.
Meanwhile, the PSNI is pursuing further investigations into the 1999 arms smuggling operation which is now believed to have been far more extensive than previously thought. One source suggested as many as 700 weapons might have been imported from the US over two years.
The PSNI is expected to apply to the High Court today for access to Garda documents on the operation. It is understood it has uncovered details of money transfers from Northern Ireland to the US to buy guns. Two men and a woman from west Belfast are under investigation for sending "in excess of Sterling £10,000" to the US for the purpose of buying guns.