A mother and son are among three people arrested as part of the investigation into the abduction and torture of Co Fermanagh man and Quinn Industrial Holdings (QIH) director Kevin Lunney.
It's understood that all three suspects arrested as part of the investigation into the savage attack on Mr Lunney had properties linked to them raided as part of the investigation last week.
Gardai arrested a Co Longford criminal, in his 40s, who is suspected of supplying cars used in the brutal crime on September 17.
A woman in her 50s, and her son, in his 20s, from Co Cavan are also being questioned about a horsebox and bleach used during the attack.
The trio are being held by gardai at stations in Cavan, Monaghan and Kells.
Mr Lunney (50) was abducted outside his home near Derrylin and taken to a horsebox across the border, where he was savagely beaten. Senior sources say officers have also received key intelligence on the Cavan duo from analysing data from mobile phones seized from the mastermind of the plot, Cyril 'Dublin Jimmy' McGuinness.
The crime boss dropped dead during a police raid at his UK safe house last week.
It was previously revealed that McGuinness recruited two Dublin-based criminals to carry out surveillance on the five directors of QIH in the weeks leading up to the abduction of father-of six Mr Lunney.
It is believed McGuinness ordered the intelligence gathering operation as he could not initially decide which of the five directors he would kidnap.
It is understood his associates used a van to conduct surveillance at the homes and workplaces of the five men to establish their routines and routes to and from work.
Other members of McGuinness' gang, believed to be about a dozen in total, were also involved in secretly monitoring the movements of QIH directors Liam McCaffrey, John McCartin, Dara O'Reilly and brothers Tony and Kevin Lunney. The attack was timed to coincide with a board meeting between the company directors and QIH's international investors, which had been due to take place in Derrylin on the morning after the attack but was cancelled.
The executives representing the company's three main financial backers, who had arrived in Dublin around the time Kevin Lunney was abducted, returned to the US after being told their security could not be assured.
A Garda spokesperson said: "An Garda Siochana continues to appeal to any person who has any information, no matter how insignificant it appears, on this vicious criminal attack or any other criminal activities which have taken place in the Cavan/Fermanagh border area over recent years to contact An Garda Siochana at Cavan Garda Station 049 4368800, the Garda Confidential Line 1800 666 111, or Crime Stoppers on 1800 25 00 25 or any Garda station."