A former Sinn Féin councillor was filmed interrogating, threatening and waterboarding a man who came to his house to buy a motorcycle.
Jonathan Dowdall, 40, and his 60-year-old father Patrick, who live on the Navan Road in Dublin, admitted at the Special Criminal Court to falsely imprisoning and threatening to kill Alexander Hurley in January 2015.
The following report contains details some readers may find distressing
Videos played in court showed Mr Hurley tied to a chair in the Dowdalls' garage as Jonathan Dowdall, who was wearing a balaclava, put a tea towel on his face and poured buckets of water over him.
Patrick Dowdall took out a silver pliers and threatened to pull off Mr Hurley's fingers, starting with the smallest.
The victim is heard pleading for his life as the Dowdalls threatened to chop him up and feed him to the dogs.
He was tied with cable ties and told "one more twist and you're dead".
The court heard that he was also told he was "a stupid dumb f**k to mess with the IRA" and that Jonathan Dowdall was a good friend of Gerry Adams and Mary Lou McDonald.
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The court also heard that Mr Hurley was a convicted fraudster.
Defence counsel said Jonathan Dowdall had searched the internet and discovered Mr Hurley had paid a man for a car with a bounced cheque.
He said he was under huge pressure and as a businessman his whole life was built on his credit rating.
He said he wanted to frighten Mr Hurley not to use his bank details but now realised he was totally 100% wrong and apologises.
In a victim impact statement, Mr Hurley said he was tortured to the point of death's door and the psychological injuries will never completely heal.
Sentencing will take place next month.