Secret MI5 documents sought by lawyers defending the alleged leader of the Real IRA Michael McKevitt were flown into Ireland this afternoon and will be examined by the Special Criminal Court tomorrow.
Detective Chief Superintendent Martin Callinan, of the Crime and Security Branch, Garda Headquarters, told the court he was concerned that certain information, if released, could put "human life at risk".
He said the IRA's track record in relation to informers was well known as was the manner in which they dealt with them.
"It is execution," he said.
It was the twelfth day of the trial of Michael McKevitt, aged 53 , of Beech Park, Blackrock, Dundalk, Co Louth.
McKevitt is charged with membership of an unlawful organisation styling itself the Irish Republican Army, otherwise the IRA, otherwise Oglaigh na hEireann between August 29, 1999 and March 28, 2001.
He is also charged directing the activities of the same organisation.
The defence is seeking to have five security documents made available to the defence team in their unedited form.
The documents have been made available, but in a heavily edited form, the court heard.
Reading from the edited version of the disclosed material, Philip McGee QC, for Mr McKevitt, submitted that the material is highly relevant and "very important" to the defence.
However, Brendan Grehan SC, prosecuting said the state has disclosed all documentation within its "power, possession and procurement" relevant to the defence.
He said this case was complicated by the fact that in his "undercover role" David Rupert, the chief witness against Michael McKevitt reported not to the gardaí but to two external powers".
The court has heard that Mr Rupert worked for MI5 and the FBI and received $1.25m for infiltrating dissident republican organisations.
In evidence, Det Chief Superintendent Callinan told the court that he was concerned that certain information, if released, could reduce the capability of the gardaí "to operate in terms of preventing and detecting subversive activity."
Justice Richard Johnson, presiding, said the court would begin examining the documents at 10.30am tomorrow.