Gardai have recovered "significant" forensic evidence from a container where they suspect businessman Kevin Lunney was tortured and beaten.
Detectives are making good progress in the investigation after a number of sheds and outhouses were searched in the Cavan area in recent days.
A main focus of the inquiry was a horse box near the village of Ballinagh where it is believed that Mr Lunney was taken following his abduction last Tuesday night.
Specialist officers from Garda Headquarters were involved in examining the horse box and sources last night said that "significant forensic evidence" was recovered.
Last night, gardai were putting plans in place to use a crane to recover the horse box and seize it as part of their investigation.
"This is a big breakthrough in the case and will assist gardai with any future proceedings," a source told the Herald. "This is the horse box gardai believe Kevin Lunney was assaulted in."
The 50-year-old Quinn Industrial Holdings (QIH) director was abducted from his home near Derrylin in Co Fermanagh before being held captive for almost three hours, and was later dumped on the side of the road near Cornafean, Co Cavan.
He is a director in a company made up of elements of the former business empire founded by ex-tycoon Sean Quinn.
Mr Quinn, at one time Ireland's richest man, has repeatedly and publicly condemned any targeting of those now running QIH.
Mr Lunney was beaten and sliced with a Stanley blade while some of his fingernails were also pulled out.
Gardai have already identified a number of suspects they believe were either directly involved or orchestrated the abduction and torture.
This includes a Cavan criminal who was captured on CCTV buying bleach which was poured over Mr Lunney in an attempt to destroy any forensic evidence.
Gardai have also increased patrols near homes of board members who have received death threats, or have been targeted, following the abduction and assault of Mr Lunney.
QIH director and chairman John McCartin said that Mr Lunney remains in Drogheda Hospital where he is "as good as you could expect him to be".
He also said Mr Lunney was "happy with the progress" he was making after surgery on his leg and that he is not expected to have any further surgery.
Investigations are continuing into death threats made against QIH directors, as well as arson attacks and other attacks on people connected to QIH.
The investigation by gardai and the PSNI into last week's assault is also trying to establish the identity of the person, or persons, who directed the gang to carry out the attack.
In a joint appeal, gardai and the PSNI are seeking help from anyone who may have seen a black Audi saloon being driven in the Derrylin, Fermanagh, Swanlinbar, Killeshandra, Cavan areas to contact them.