The DPP is investigating as a matter of urgency the feasibility of taking a prosecution under the Geneva Convention against the US-based prime suspect for the murder of two Irish soldiers in Lebanon 25 years ago.
Privates Thomas Barrett and Derek Smallhorne were shot dead in 1980 at the village of At Tiri in south Lebanon after their UN convoy was stopped by armed members of a Lebanese militia.
No one has ever been charged with the killings but a Lebanese-born man who is now a naturalised US citizen is regarded as the chief suspect by the Department of Defence.
A department spokesman said yesterday that a reply from the DPP on the potential application of the provisions of the Geneva Convention was awaited.
"Because of the complexities involved it may take some time," he said.
Earlier this year, Defence Minister Willie O'Dea ordered that the files on the murders be reopened to establish if charges could be brought.
Mr O'Dea also said he would leave "no stone unturned" in seeking justice for the two privates.
His officials have been consulting the Department of Foreign Affairs and the office of the Attorney General as part of a review of international law.
Attorney General Rory Brady has advised there are no provisions in Irish law to pursue a prosecution against the alleged killer.
"The attorney did indicate, however, that while untested and potentially difficult, it might be possible for Ireland to pursue a prosecution under the provisions of the Geneva Conventions.
"While this appears an outside possibility, I have asked the DPP, who would be responsible for pursuing any prosecution, to review the matter as a matter of urgency," said Mr O'Dea.
At the same time the Lebanese and US authorities have been contacted to inform them of Ireland's "earnest desire and determination" to have the alleged perpetrator made accountable and to promise them assistance if they are able to bring him to justice.
"However, the long passage since the tragic incident will create its own difficulties in mounting a prosecution, even if we can make the alleged perpetrator amenable to justice," Mr O'Dea said.
Lebanon is the country with prime jurisdiction in the case but there is no extradition agreement between Lebanon and the US.
Another possible way of bringing charges is through the Convention on the Safety of UN and Associated Personnel which was designed to protect blue-helmet personnel.
However it only came into force in 1999 and does not apply retrospectively.