The independent expert who oversaw the sale of Siteserv for IBRC said Denis O'Brien's offer was accepted because it was the best, simplest and could be completed.
Speaking on RTÉ's Prime Time, Walter Hobbs said that when he began dealing with the transaction €100m was already gone and the question was if they could rescue the other €50m.
He said he believed the higher bid that came in from the French company Altrad was designed to disrupt the bidding process, because of competitive concerns that the company had.
Mr Hobbs said initially the bid from Denis O'Brien was the highest and was accompanied by a three-page letter, while other offers had multiple terms and conditions attached to them.
He said the O'Brien offer was accepted, because they believed it could be completed in a limited time, at an agreed price, and with no major difficulties.
Mr Hobbs said a number of other bidders were excluded because of the nature of the Siteserv business.
He said as Siteserv owned so many different types of businesses it would have been difficult to sell to trade buyers and they therefore focused on conglomerate buyers.
He said the Department of Finance has never spoken to him about the transaction but that he had given comprehensive memos to the board about the key stages of the deal.
He said the reason shareholders were paid €5m was because they were not going to let a deal go through where they got zero.
Mr Hobbs said if the deal collapsed, 1,500 people would have lost their jobs and IBRC would have lost €45m.
"People had votes, they had the power and they had to be bought. It was better than losing the whole thing wasn't it?" he said.
He said his last advice to IBRC on the deal was that "pursuing any other route at this stage would be highly perilous".
Calls for independent inquiry into Siteserv sale
Independent TD Catherine Murphy has said there should be an independent inquiry into the sale of Siteserv.
Speaking on RTÉ's Six One News, Ms Murphy said the new documents released to her about the sale show there was a clear difference between what the Department of Finance and IBRC thought about the deal.
Ms Murphy, who originally raised questions about the transaction, said whoever carries out the inquiry needs to be carefully selected because "it's a small town" and there could be conflicts of interest.
The TD said there were already conflicts in terms of some of the people who had oversight of the transaction.
She said the main questions she would like answered is why trade buyers were excluded from purchasing the same and why the higher bids for the company were not accepted.
New Freedom of Information data released to Ms Murphy outlines the reasons why the Department of Finance questioned aspects of the Siteserv deal.
In relation to why Siteserv was allowed to run the sales process, the department said IBRC could have run the process itself.
While IBRC argued to do so would have created the impression of a "distressed sale", the department said while it cannot say whether this would have been damaging, the decision to allow Siteserv run the process was central to everything that followed.
On the decision to exclude trade buyers, the department said a trade buyer may have been in a position to provide the best price.
IBRC said allowing trade buyers opened the prospect of people reviewing data with no intention of bidding.
On the controversial payment of €5m to shareholders in Siteserv, the department said "arguably no payment should have been made to shareholders" given the position the company was in.
They question whether it was correct to accept advice from Davy's Stockbrokers on this given they were advisers to Siteserv.
IBRC said the payment was necessary to secure the sale and that examinership was not an option because it would have breached customer contracts.
IBRC said it did not have the ability to negotiate with the shareholders.