A man in his 30s arrested on Thursday in relation to the abduction and assault of Co Fermanagh businessman Kevin Lunney has been released without charge.
Mr Lunney, a director at Quinn Industrial Holdings (QIH), was abducted outside his home near Derrylin, Co Fermanagh last September and later assaulted and tortured.
For almost a decade executives and companies involved in the management or acquisition of assets formerly owned by former billionaire Sean Quinn have been subjected to a campaign of violence. Mr Quinn has condemned the violence and has said that those carrying it out were not acting in his name.
The arrested man had been held at Cavan Garda station under Section 50 of the Criminal Justice Act 2007.
A file will now be prepared for the Director of Public Prosecutions and investigations are continuing.
On Friday, the Police Service of Northern Ireland (PSNI) released three people who were also arrested in connection with the investigation.
Two men, aged 23 and 61, and one woman aged 61 were detained in the Fermanagh area on Thursday on suspicion of conspiracy to kidnap, conspiracy to cause grievous bodily harm with intent, and assisting offenders.
The Police Service of Northern Ireland (PSNI) announced their unconditional release from custody in Omagh police station on Friday.
The four arrests were part of a joint investigation between the PSNI and An Garda Síochána.
Anyone with information can contact police at Enniskillen on the non emergency number 101, quoting reference 1748 17/09/19 or Crimestoppers on 0800 555 111.
The Garda can be contacted at Cavan Garda station (049 4368800), the Garda confidential line (1800 666 111), Crimestoppers (1800 25 00 25) or any Garda station.