The British Army officer involved in Green's killing was murdered by whom? 
John Francis Green:  According to Secret Intelligence Service operative Captain Fred Holroyd, British Army Captain Robert Nairac was involved in Green's killing. Robert Nairac: Captain Robert Laurence Nairac GC (31 August 1948 –15 May 1977) was a British Army officer who was abducted from a pub in Dromintee, south County Armagh, during an undercover operation and murdered by the Provisional Irish Republican Army (IRA) on his fourth tour of duty in Northern Ireland as a Military Intelligence Liaison Officer.
Provisional Irish Republican Army