Thursday's charges were the first filed over the slaying of 52-year-old David Black. He was shot dead Nov. 1 as he drove to work at Northern Ireland's main prison.
Black was the first prison guard killed in nearly two decades in the British territory. While the major Provisional IRA faction renounced violence and disarmed in 2005, IRA splinter groups still mount occasional bombings and shootings.
Police say a 36-year-old suspect from Northern Ireland was spotted in surveillance TV footage crossing the Irish border to collect the car used by the attackers. A 44-year-old Dublin man was being arraigned later Thursday on similar charges.