A number of searches by gardaí investigating issues at Anglo Irish Bank were unlawful and unconstitutional.
The disclosure was made on the first day of evidence at the trial of former Anglo Irish Bank chairman Seán FitzPatrick (68) on charges of misleading auditors about loans of up to €100m he received from the bank.
But despite the unlawful nature of the searches, a jury was told Dublin Circuit Criminal Court had ruled they could still be shown documents seized using the warrants.
The court heard about two warrants for searches at the headquarters of Irish Nationwide Building Society and five warrants for searches at Anglo's headquarters and another Anglo building in Dublin. These led to large quantities of documents and electronic material being seized in 2009 and 2010.
The court heard evidence from three garda officers who were involved in the searches.
One of them, Detective Sergeant Brian Mahon, testified that warrants were secured from the District Court in order to gain access to Irish Nationwide and Anglo premises.
But under cross-examination from the defence, he agreed that those searches had been deemed by the court to be unlawful.
"All of the entries were ruled by the court to be unlawful and unconstitutional, but it will have no consequence in terms of the jury receiving the documents," the defence said.
Details of further searches which were subsequently deemed by the court to be unlawful were also outlined by two other garda witnesses.
However, the court has decided that documents obtained in these other searches can also be put before the jury.
Sergeant Karl Moriarty testified about serving production orders on Irish Nationwide and Anglo in 2011 while on secondment at the Office of the Director of Corporate Enforcement.
These required the two institutions to produce certain documents and material in relation to bank accounts.
The information sought included the beneficiaries of certain accounts, bank statements, and details of cheques and payments drawn from those accounts.
The witness said the orders led to many thousands of documents being produced.
Following his evidence, the prosecution said there was a legal issue that needed to be dealt with and Judge John Aylmer excused the jury until this morning.
The judge told the jurors not to seek out information about the case anywhere outside the court and warned them against seeking information on the internet and social media.
Mr FitzPatrick, of Whitshed Road, Greystones, Co Wicklow, has pleaded not guilty to 27 charges he is facing.
Yesterday was the first day jurors have heard evidence in the case, which is entering its 59th day.
Jurors were previously informed that evidence had been delayed due to a number of legal matters which needed to be decided upon in their absence.