Question: The British Army officer involved in Green's killing was murdered by whom? 
Context: John Rodgers Meigs (February 9, 1842 – October 3, 1864) was an officer in the Union Army during the American Civil War.  He was the son of Brigadier General Montgomery C. Meigs, the Quartermaster General of the United States Army.  He participated in the First Battle of Bull Run, and later testified in the court-martial trial of an officer involved in the retreat from the battle.  He attended the United States Military Academy, where he was an acting assistant professor of mathematics and graduated first in his class in June 1863.  He was lauded by Secretary of War Edwin M. Stanton for strengthening the defenses of Baltimore, Maryland; was an engineer and acting aide-de-camp on the staff of Brigadier General (Volunteers) William W. Averell; was Chief Engineer of the Shenandoah Valley for the Department of West Virginia; and was Chief Engineer of the Middle Military Division and aide-de-camp to General Phillip Sheridan.  The circumstances under which Meigs died led to the burning of Dayton, Virginia, in retaliation.  His funeral was a public event attended by President Abraham Lincoln, Stanton, and numerous government dignitaries.  A book of Meigs' letters were published in 2006 under the title "A Civil War Soldier of Christ and Country: The Selected Correspondence of John Rodgers Meigs, 1859-64". John Francis Green (18 December 1946 – 10 January 1975), was a leading member of the North Armagh Brigade of the Provisional Irish Republican Army, holding the rank of Staff Captain and Intelligence Officer.  He was killed in a farmhouse outside Castleblayney, County Monaghan, by members of the Mid-Ulster Brigade of the Ulster Volunteer Force (UVF).  According to Secret Intelligence Service operative Captain Fred Holroyd, British Army Captain Robert Nairac was involved in Green's killing.  Green's was one of the 87 killings attributed by the Pat Finucane Centre to the group of loyalist extremists known as the Glenanne gang.  No one was ever prosecuted for the killing. Sidney Langford Hinde, (23 July 1863 - 18 October 1930), Chevalier de l'ordre royal du lion; Membre honoraire de la Société belge de géographie; Medical Officer of the Interior, British East Africa; Late Captain, Congo Free State Forces; was a military medical officer involved in colonial operations in the Congo and East Africa in the 19th century. General Sir Frank Douglas King, (9 March 1919 – 30 March 1998) was a British Army officer who served as General Officer Commanding (GOC) of the British Army in Northern Ireland at the height of the Troubles.  He held a number of other senior posts in the British Army, having begun his military career in the ranks during the Second World War. Thomas Sutcliffe (c. 1790 – 22 April 1849) was an English soldier of fortune.  After periods in the Royal Navy and then as an army officer involved in the Battle of Waterloo, he became an army officer in the service of Colombia and then Chile.  In later years he was a writer. 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.  He was posthumously awarded the George Cross in 1979. An ammunition technical officer (ATO) is an officer involved in all aspects of the army's use of ammunition.  This includes: bomb disposal, clearance of ERW, explosives accident investigation, procurement, in service management, storage, and inspection and repair. Lieutenant Colonel Rupert Stuart Michael Thorneloe, MBE (17 October 1969 – 1 July 2009) was a British Army officer who was killed in action on 1 July 2009 near Lashkar Gah, Helmand Province in southern Afghanistan.  s of 2009 , Thorneloe is the highest-ranking British Army officer to have been killed in action since Lieutenant Colonel H. Jones's death in 1982 during the Falklands War. General Sir Nicholas Patrick "Nick" Carter, {'1': ", '2': ", '3': ", '4': "} (born 11 February 1959) is a senior British Army officer.  He served as commanding officer of 2nd Battalion, Royal Green Jackets in which role he was deployed to Bosnia in 1998 and Kosovo in 1999.  After service in Afghanistan, he took command of 20th Armoured Brigade in 2004 and commanded British forces in Basra.  He was subsequently appointed General Officer Commanding 6th Division, which was deployed to Afghanistan with Carter as Commander ISAF Regional Command South, before he became Director-General Land Warfare.  After that he became Deputy Commander Land Forces in which role he was the main architect of the Army 2020 concept.  After a tour as Deputy Commander, International Security Assistance Force, he assumed the position of Commander Land Forces in November 2013.  In September 2014, he became head of the British Army as Chief of the General Staff succeeding General Sir Peter Wall. Raymond Durie of Durie (10 August 1905 – 29 March 1999), until 1988 known as Raymond Dewar-Durie, was a British army officer involved in the Yangtze incident who later became chief of the Clan Durie.
Answer: Provisional Irish Republican Army