One of the people arrested by gardai investigating the attempt to send guns in the post from Florida to Ireland is believed to be a senior Provisional IRA figure close to the organisation's so-called quartermaster-general.
The 39-year-old man, who lives in south Cavan, was held in Monaghan Garda station for two days last weekend. His arrest followed the discovery of a .357 Magnum revolver in a package being sent to an address in Co Meath and which he was expected to collect.
After his arrest under the Offences Against the State Act, the man, who was held for questioning for two days, did not utter a single word. He also refused all food and drink while in the station.
Gardai from the Crime and Security Branch at Garda Headquarters and local Special Branch officers searched his house and found two fake passports, one bearing the picture of another Provisional IRA figure in Belfast, and two driving licences.
The Provisional IRA quartermaster-general is the figure who would have control of any arms importation exercises although he might not be directly involved.
However, amid increasing signs that members of the IRA were involved in the Florida operation, senior security sources were last night still not prepared to state categorically that the organisation was behind the plot to bring possibly hundreds of weapons into the State.
Gardai in Mill Street station in Galway, meanwhile, are still holding a 54-year-old United States citizen, with an address in San Francisco, who arrived in Connemara earlier this week and booked into a hotel.
It is understood this man made a number of calls to a mobile telephone in the house in Inverin where six handguns and ammunition were found during a Garda raid on Wednesday.
The American had apparently flown to Ireland from the west coast of the US. It is understood he is refusing to answer any questions from gardai who have discovered the man travels widely and has connections in Central and South America.
It is known that one of the men arrested by the FBI in Florida earlier this week had recently travelled to Mexico. It is also under stood this man told FBI agents he had intended to travel to Ireland earlier this week - it is thought for a rendezvous in connection with the arms-smuggling plot.
Last night a Co Galway woman appeared in the Special Criminal Court charged in connection with the attempt to smuggle arms into the country. A Belfast man, who had been arrested with the woman at the house she was renting in Inverin, was released by gardai without charge yesterday.
The Belfast man is a brother of one of the men arrested by the FBI in Florida. The wife of the man released in Galway yesterday had been held briefly on Wednesday but was released after only a few hours in custody.
Four people - three Belfast men and a Co Cork woman - arrested by the FBI in connection with the arms smuggling plot remain in prison in Florida and will face trial there.
Asked about the involvement of Provisional IRA figures in the smuggling plot and evidence in Florida on Thursday when a court heard the arms were being sent to the IRA, senior Garda and Government sources continued to say there was conflicting evidence suggesting links to dissident republicans and even criminal sources.
However, there was no clear information about these links last evening.
Another factor giving rise to concern about the Provisional IRA's intentions is the murder in Belfast early yesterday of a young north Belfast Catholic man who was kidnapped, interrogated and possibly tortured for a number of days and then shot dead just off the Falls Road.
Local sources say they believe the Provisional IRA was responsible for killing Mr Charles Bennett (22) a part-time taxi-driver, though the reason for his murder was unclear.
Mr Bennett left the home of his girlfriend on Clifton Park Avenue in north Belfast at 6.20 p.m. on Sunday. Answering a call to the door, he appeared to know the callers and told her he would be back shortly, but never returned.
Two shots were reported by residents in Milltown Row off the Falls Road at about 1.05 a.m. yesterday and Mr Bennett's body was discovered a short time later in the car-park at the rear of St Galls GAA Club.
While senior Garda sources say there is insufficient evidence to tie the Provisionals firmly into the importation plot, other Garda sources disagree. They point out that as well as there being a number of Provisionals involved, the methodology is very reminiscent of past IRA smuggling plots.
In the past, a large percentage of guns smuggled by the Provisional IRA, including as many as seven large sniper rifles, came through the post from the US. The Provisional IRA also used "drop" addresses in locations similar to those used in the Florida smuggling operation.