Four people have been arrested in connection with the abduction of Quinn Industrial Holdings director Kevin Lunney.
Mr Lunney was kidnapped and brutally assaulted by a group of masked men last September.
The attack was the most serious act in a campaign of intimidation against executives at QIH that has been ongoing for several years.
As part of the investigation into the abduction and attack, three people have been arrested in the North while one man was arrested here in the Republic.
Gardaí say a man in his 30s is being held at Cavan Garda Station in relation to the abduction and assault for an offence contrary to section 72 Criminal Justice Act 2006.
The PSNI, meanwhile, arrested two men - aged 23 and 61 - and one woman - aged 61 - in the Fermanagh area.
They are being questioned at Omagh police station on suspicion of conspiracy to kidnap; conspiracy to cause Grievous Bodily Harm with Intent and assisting offenders.
In a statement, Chief Superintendent John O Reilly of the Cavan/ Monaghan Garda Division said: "Today’s arrests demonstrate An Garda Síochána’s ongoing commitment, working closely with the Police Service of Northern Ireland, and is a further significant step to ensuring that the perpetrators of this vicious attack will be brought to justice.”
Anyone with any information about the abduction is being asked to contact Cavan Garda Station on 049-436-8800, the Garda Confidential Line on 1800-666-111, Crimestoppers on 1800-25-00-25 or any Garda station.