Twenty-four Irish police officers are to be called to appear at the Omagh bomb civil case.
Twenty-nine people were killed in the Omagh bomb
The judge hearing the case said a letter would be issued to the judicial authorities in Dublin, requesting their help to secure the evidence.
However, Mr Justice Morgan said public interest immunity difficulties may prevent the officers testifying in NI.
Relatives of some of the 29 victims are suing five men in a multi-million pound compensation action beginning in April.
The Omagh families £14m civil case has been taken against convicted Real IRA leader Michael McKevitt and four other men: Seamus Daly, Liam Campbell, Colm Murphy and Seamus McKenna.
The trial is expected to last up to two months.