Question: What German ace-of-aces was shot down by Cedric Bassett Popkin during World War 1?

full_context: Document 1: Snowy Evans: Willy John "Snowy" Evans (  1891 –1925) was a Lewis machine gunner in the Royal Australian Artillery (RAA) during World War I. Unsolved History, produced by Discovery Channel credited him with firing the shot that killed Manfred von Richthofen ("The Red Baron"), near Vaux-sur-Somme, France on 21 April 1918. However, most sources attribute the feat to Sergeant Cedric Popkin of the 24th Machine Gun Company. Other sources have suggested that Gunner Robert Buie, also of the 53rd Battery, fired the fatal shot, but there is now little support for this theory.
Document 2: Cedric Popkin: Cedric Bassett Popkin (Born 20 June 1890, died 26 January 1968) is considered the person most likely to have killed German ace Manfred von Richthofen — also known as the "Red Baron" — on 21 April 1918. Popkin was an anti-aircraft (AA) machine gunner with the First Australian Imperial Force (AIF), during World War I.
Document 3: Bolko von Richthofen: Bolko von Richthofen (September 13, 1899 – March 18, 1983) was a German archaeologist and a distant relative of the family of Manfred von Richthofen, the "Red Baron". He is sometimes confused with his distant cousin and namesake, Karl Bolko von Richthofen (1903–1971) – the youngest brother of the fighter ace.
Document 4: Manfred von Richthofen (sports official): Manfred von Richthofen (4 February 1934 – 1 May 2014) was a German hockey player and coach. He was also an honorary President of German's national Olympic federation. He was the nephew of World War I German pilot Manfred von Richthofen (the "Red Baron"). His career began during the 1950s. He retired in 2006. Richthofen was born in Berlin, Germany.
Document 5: Hermann von Richthofen: Hermann Freiherr von Richthofen, GCVO (born 20 November 1933 in Breslau) is a German diplomat. He is a great nephew of Manfred von Richthofen, the "Red Baron".
Document 6: Robert Saundby: Air Marshal Sir Robert Henry Magnus Spencer Saundby {'1': ", '2': ", '3': ", '4': "} (26 April 1896 – 25 September 1971) was an RAF officer whose career spanned both World War I and World War II. He distinguished himself gaining five victories during World War I, and was present during the air battle when Lanoe Hawker was shot down and killed by Manfred von Richthofen, the "Red Baron". He is chiefly remembered for his role as Deputy AOC in C Bomber Command under Sir Arthur 'Bomber' Harris during the latter part of World War II.
Document 7: List of victories of Werner Voss: Leutnant Werner Voss (13 April 1897 – 23 September 1917) was a friendly rival of World War I's leading ace, Manfred von Richthofen. Richthofen himself considered Voss as the only pilot with the potential to exceed Richthofen's aerial victory score. When Voss was killed in action, he had scored 44 victories. As can be seen by the list below, his victory roll is well documented.
Document 8: Erich Hartmann: Erich Alfred Hartmann (19 April 1922 – 20 September 1993), nicknamed "Bubi" ("The Kid") by his German comrades and "The Black Devil" by his Soviet adversaries, was a German fighter pilot during World War II and the most successful fighter ace in the history of aerial warfare. He flew 1,404 combat missions and participated in aerial combat on 825 separate occasions. He claimed, and was credited with, shooting down 352 Allied aircraft—345 Soviet and 7 American—while serving with the "Luftwaffe". During the course of his career, Hartmann was forced to crash-land his fighter 14 times due to damage received from parts of enemy aircraft he had just shot down or mechanical failure. Hartmann was never shot down or forced to land due to enemy fire.
Document 9: Manfred von Richthofen (general): Karl Ernst Manfred Freiherr von Richthofen (24 May 1855 – 28 November 1939) was a German "General der Kavallerie" (General of the Cavalry) during World War I and recipient of the order Pour le Mérite, known informally as the Blue Max. Richthofen was a great uncle of his more famous namesake Manfred von Richthofen, known as the Red Baron, who was his godson and named after him.
Document 10: Lanoe Hawker: Lanoe George Hawker VC, DSO (30 December 1890 – 23 November 1916) was a British First World War flying ace. Having seven credited victories, he was the third pilot to receive the Victoria Cross, the highest decoration for gallantry awarded to British and Commonwealth servicemen. He was killed in a dogfight with the famous German flying ace Manfred von Richthofen ("The Red Baron"), who described him as "the British Boelcke".
Document 11: Max Immelmann: Max Immelmann (21 September 1890 – 18 June 1916) "PLM" was the first German World War I flying ace. He was a pioneer in fighter aviation and is often mistakenly credited with the first aerial victory using a synchronized gun. He was the first aviator to win the "Pour le Mérite", and was awarded it at the same time as Oswald Boelcke. His name has become attached to a common flying tactic, the Immelmann turn, and remains a byword in aviation. He is credited with 15 aerial victories.
Document 12: The Red Baron (2008 film): The Red Baron (aka Der rote Baron (original title)) is a 2008 German-British biographical action war film written and directed by Nikolai Müllerschön about the World War I fighter pilot Manfred von Richthofen, known as the "Red Baron". The film stars Matthias Schweighöfer, Joseph Fiennes, Til Schweiger and Lena Headey. "The Red Baron" was filmed entirely in English to improve its international commercial viability.
Document 13: Lothar von Richthofen: Lothar Freiherr von Richthofen (born Lothar Siegfried Freiherr von Richthofen; 27 September 1894 – 4 July 1922) was a German First World War fighter ace credited with 40 victories. He was a younger brother of top-scoring ace Manfred von Richthofen (the "Red Baron") and a distant cousin of Luftwaffe Field Marshal Wolfram von Richthofen.
Document 14: Manfred von Richthofen: Manfred Albrecht Freiherr von Richthofen (2 May 1892 – 21 April 1918), also known as the "Red Baron", was a fighter pilot with the German Air Force during World War I. He is considered the ace-of-aces of the war, being officially credited with 80 air combat victories.
Document 15: Eddie Rickenbacker: Edward Vernon Rickenbacker (October 8, 1890 – July 23, 1973) was an American fighter ace in World War I and Medal of Honor recipient. With 26 aerial victories, he was America's most successful fighter ace in the war. He was also considered to have won the most awards for valor by an American during the war according to the April 2017 VFW magazine in their special World War I edition.
ground_truth: Manfred von Richthofen