Jim Mansfield Jnr arranged meetings with the New IRA and the INLA, who were to "assist" in getting back parts of his family's former property portfolio, the Special Criminal Court has heard.
Martin Byrne, who is now in the Witness Protection Programme, told the non-jury court that he had asked Mr Mansfield if he realised how dangerous these people were.
However, the witness testified that the accused replied that he "did not care" and "was going to get back what was his".
Mr Byrne gave evidence yesterday in the Special Criminal Court trial of Mr Mansfield (53), of Tasaggart House, Garters Lane, Saggart, Co Dublin.
The accused is charged with conspiring with one or more persons to falsely imprison Mr Byrne on a date unknown between January 1, 2015 and June 30, 2015, both dates inclusive.
He is also charged with attempting to pervert the course of justice by directing Patrick Byrne to destroy recorded CCTV footage, with the alleged intention of perverting the course of public justice in relation to the false imprisonment of Martin Byrne at Finnstown House Hotel, Newcastle Road, Lucan, Co Dublin between June 9, 2015 and June 12, 2015.
Mr Mansfield has pleaded not guilty to both counts on the indictment.
Giving evidence from the jury box where two security men were present, Mr Byrne described the events leading up to June 9, 2015.
In his evidence, Mr Byrne, a security professional, said Saggart Lodge Court, a piece of land known as "Paddy Reilly's Field" which was at the back of the Citywest Hotel and Finnstown House Hotel, went into receivership.
A third party was brought in to act on behalf of the family as Mr Ferris, a receiver who took over Citywest Hotel around 2011, did not want to deal with Mr Mansfield Snr directly, he said. A financial backer then helped the third party buy the property from the receiver.
Mr Byrne said it was understood that money was to be paid by the accused to the third party to buy back "Paddy Reilly's Field" but this was never paid over, which led to a fall out between Mr Mansfield and the third party.
The witness said he was asked to meet with members of the New IRA "to assist the accused" in getting back "Paddy Reilly's Field".
In May 2015, Mr Byrne said he went to a meeting in Keatings Park in Rathcoole with the accused to get Tasaggart House and The Towers signed back over to Mr Mansfield Jnr.
When he got to the meeting, Dessie O'Hare and Declan Duffy were in the reception area, he said.
Mr Byrne said he told the two men that the accused was dealing with the INLA and the Real IRA and he did not think they should continue with the meeting.
Mr Byrne said Duffy asked him which IRA he was talking about and he told him the one under the leadership of another named man. O'Hare and Duffy then left the room, he said.
Following that meeting, Mr Byrne said he asked Mr Mansfield Jnr if he realised how dangerous these people were.
"He said at that point he did not care and he was going to get back what was his," the witness said.
In June 2015, the witness said Mr Mansfield Jnr organised a meeting with O'Hare at Keatings Park.
Mr Byrne arrived with the accused and they met O'Hare who shook hands with Mr Mansfield Jnr. Mr Byrne followed them into an upstairs office and then Declan Duffy arrived.
"I was surprised because I didn't see any reason for him to be there," Mr Byrne said.
The witness said O'Hare told Mr Mansfield: "You're done here now, you can leave."
He said O'Hare told him his services were no longer required.
Then Duffy shouted and five other men arrived, he said.
He said he was escorted downstairs with three men in front and four behind.
He said he felt he was not able to leave and when he asked for time to make his own way home, they refused.
Once downstairs, he said he could see Mr Mansfield Jnr standing out the front.
"At that point I believed he had set me up and knew what was happening. I said to him, 'you set me up,' and the guys came from behind and grabbed me," Mr Byrne told the court.
He said Mr Mansfield Jnr was "a couple of feet away" as one of the seven men emptied his pockets, taking cash, a bank card, his watch and telephone.
He said he was put into the back of a navy Honda with one man on either side, one in the passenger seat and the driver.
"I could not leave," he said.
O'Hare came to the car and handed the driver a piece of paper with Mr Byrne's address on it, said Mr Byrne.
When Mr Byrne asked to be let go so he could get his wife and son out of his house he said the man in the front passenger seat punched him on the left side of the face with a closed fist and told him to shut up.
The group of seven men and Mr Byrne travelled in convoy in a Ford Mondeo, the Honda and a white Transit van to the Towers where Mr Byrne was struck a second time by the same man, he said.
When they went inside, having broken through a security gate, Mr Byrne's wife was there with their son. All seven men went into Mr Byrne's home. BEAT
When a security man knocked on the door the gang grabbed him and pulled him inside.
O'Hare, Duffy and another man got the security guard on the ground and beat him up, the witness said.
They then picked him up and brought him to another house, before O'Hare told the witness: "Let's go, it's your turn."
Mr Byrne was struck and suffered a burst eardrum and would later require stitches.
On a CCTV monitor he saw a red unmarked garda car that he knew from the area, pulling up outside. He said he saw a chance to escape and told O'Hare he would get rid of the gardaí.
When Mr Byrne went outside he alerted gardaí and within minutes a garda helicopter and squad cars were at the scene.
The trial continues on Monday before Mr Justice Alexander Owens presiding, sitting with Judge Sinéad Ní Chulacháin and Judge James Faughnan.