Two loyalist supergrasses were interviewed 330 times by police before their evidence was used in a trial, the North's justice minister said today.
The supergrass system of offering lower sentences to criminals in exchange for information was widely criticised after the acquittal last week of 12 men, nine charged with the murder of Ulster Defence Association leader Tommy English.
Stormont justice minister David Ford gave evidence about the trial today before his assembly scrutiny committee.
"None of these are easy decisions, not least because they involve predicting how human beings are going to behave," he said.
"The judge must apply a high standard to the evidence put in any case in determining if it proves the case beyond reasonable doubt."
Ulster Volunteer Force members Robert and Ian Stewart had given evidence against 13 men.
They admitted UVF membership, and had already served more than three years for their part in the murder of Mr English on Halloween night 2000.
The Ulster Defence Association member was shot dead in front of his wife and children at his home on Belfast's Ballyduff estate at the height of a loyalist feud between the UVF and UDA.
The Stewart brothers each had their sentences reduced by 19 years after admitting involvement in the murder of Mr English and agreeing to give evidence against their alleged accomplices.
Trial judge Mr Justice John Gillen said they lied to the police and the court. The Public Prosecution Service is reviewing the case.
Mr Ford said: "How an individual deals with interviews by police in one set of circumstances may be very different to how they stand up to cross-examination by the defence barristers in the courtroom."
Former Police Ombudsman Baroness Nuala O'Loan and a London barrister were involved shortly before the case went to court, Mr Ford said.
The police investigation, Operation Ballast, now known as Operation Stafford, was launched after Baroness O'Loan's investigation into allegations of collusion between police officers and the Mount Vernon unit of the UVF.
She found evidence that some loyalists had been special branch agents and that police had colluded with them to protect their arrest and prosecution.
Northern Ireland's director of public prosecutions Barra McGrory has explained why the English trial went ahead.
Mr McGrory said the brothers had gone voluntarily to a police station at a time when there was no evidence against them and had provided information about the murder of Tommy English which was consistent with information held by the police.
He said police had then carried out an extensive debriefing exercise and concluded that both brothers had given "truthful and reliable accounts".
Sinn Féin MLA Raymond McCartney told the committee: "There are people out there saying that this (supergrass trial) is a continuation of a flawed system and we will find ourselves back in a situation which we find ourselves in before where we had a review of the criminal justice system."