A senior Garda today told of his "great concerns" for the safety of the chief prosecution witness in the trial of Mr Michael McKevitt on charges of directing terrorism.
Det Chief Supt Martin Callinan, head of the Garda Siochána intelligence and security section, said he feared for the safety of Mr David Rupert, the US citizen set to be the chief witness against Mr McKevitt.
He also told the Special Criminal Court of a three-decades-old security file on Mr McKevitt, the alleged leader of the "Real IRA".
Det Chief Supt Callinan told a preliminary hearing linked to the trial that given the information he had, the threat to Mr Rupert's life was "a very real and very substantive one".
He added that he knew of "extreme efforts" by members the "Real IRA" to locate Mr Rupert and members of his family.
Mr Callinan also said the exposure of names of personnel from the FBI and the British security services, who have provided sworn affidavits in the case against Mr McKevitt, would "place their lives in real danger".
Mr McKevitt (51), from Dundalk, Co Louth, is the first person to face charges of directing terrorism under the terms of legislation introduced by the Government in response to the 1998 bombing of Omagh, when 29 people died and over 200 were injured.
He is also accused of membership of an illegal organisation.