According to journalist Toby Harnden, the British Military Intelligence assessment was that the attack was carried out by local IRA members "who were acting outside the normal IRA command structure". According to Harnden, RUC files suggest that 14 IRA members – including future 'Real IRA' leader Michael McKevitt – had met on New Year's Eve to plan the attack. Harnden quotes an alleged South Armagh IRA member, "Volunteer M", who said that "IRA members were ordered by their leaders to carry out the Kingsmill massacre". Harnden also quotes Sean O'Callaghan, an IRA member who worked for the security forces as a double agent. O'Callaghan claims that IRA Chief of Staff, Seamus Twomey, authorised the attack after Brian Keenan argued it was the only way to prevent more Catholics being killed. However, O'Callaghan says the two men did not consult the IRA Army Council about the attack. Ruairí Ó Brádaigh claims that he and Twomey only learned of the Kingsmill attack after it had happened. According to a police intelligence report, the IRA Army Council reprimanded the South Armagh Brigade six weeks before the massacre for carrying out sectarian killings.