Pearse McAuley (32), the IRA member from Strabane, Co Tyrone, who jumped bail as he faced an appeal against extradition to Britain, will appear in the High Court today.
Until late last night he was being detained in Henry Street Garda Station, Limerick, under Section 30 of the Offences Against the State Act.
He was being questioned as part of the continuing inquiry into the murder of Det Garda Jerry McCabe in an aborted post office raid in Adare, Co Limerick, in June 1996.
Garda McCabe's colleague, Det Garda Ben O'Sullivan, was seriously injured in the incident.
McAuley was arrested in a house in Renvyle, Connemara, Co Galway, at the weekend with two others and can be held for 48 hours.
He and Nessan Quinlivan, from Limerick, escaped from Brixton prison after shooting a prison officer in 1991 and both were captured in Dublin and Tipperary by the Garda Emergency Response Unit.
A 26-year-old man, who was also arrested in Galway, is being detained in Roxboro Garda Station in Limerick and a woman in her 30s, who was arrested with McAuley, is being detained in Henry Street Garda Station.
Garda sources described McAuley's arrest as "a very significant breakthrough" in their investigations in Det Garda McCabe's murder.
Two other men have already been charged with his murder.