Question: Who did Jim Skardon interrogate that was an atomic spy?

Context articles: Atomic Blonde
Joel Barr
Theodore Hall
Jim Skardon
Douglas Mackiernan
Klaus Fuchs
The IPCRESS File
David Greenglass
Mark Strauss (journalist)
Ruth Greenglass

Atomic Blonde is a 2017 American action spy thriller film directed by David Leitch, in his first solo directorial credit, and written by Kurt Johnstad.
 It is based on Antony Johnston and Sam Hart's 2012 graphic novel "The Coldest City", published by Oni Press, which revolves around a spy who has to find a list of double agents who are being smuggled into the West, on the eve of the collapse of the Berlin Wall in 1989.
 The film stars Charlize Theron and James McAvoy, with John Goodman, Til Schweiger, Eddie Marsan, Sofia Boutella, and Toby Jones in supporting roles.
Joel Barr (January 1, 1916 – August 1, 1998), also Iozef Veniaminovich Berg and Joseph Berg, was part of the Soviet Atomic Spy Ring.
Theodore Alvin Hall (October 20, 1925 – November 1, 1999) was an American physicist and an atomic spy for the Soviet Union, who, during his work on US efforts to develop the first and second atomic bombs during World War II (the Manhattan Project), gave a detailed description of the "Fat Man" plutonium bomb, and of several processes for purifying plutonium, to Soviet intelligence.
 His brother, Edward N. Hall, was a rocket scientist who worked on intercontinental ballistic missiles for the United States government.
William James Skardon (1904–1987) was a Special Branch officer who became an MI5 interrogator and head of "The Watchers" (physical surveillance teams).
 He was intimately involved with the investigation of the Cambridge Five and the interrogation of Klaus Fuchs.
Douglas Seymour Mackiernan (April 25, 1913 – April 29, 1950) was the first officer of the Central Intelligence Agency (CIA) to be killed in the line of duty.
 He worked as a cryptographer for the United States Army Air Forces and was then posted to China as an Air Force meteorologist during World War II.
 By 1947, he had quit the Air Force and was employed as a covert intelligence officer by the CIA.
 As a cover for that work he was assigned the position of Vice-Consul for the U.S. State Department at its consulate in Ürümqi (Tihwa) in East Turkestan (modern Xinjiang).
 There his scientific talents (he dropped out of the Massachusetts Institute of Technology after his freshman year) were employed in espionage.
 Until 2002, the CIA successfully hid the fact that Mackiernan was America's first atomic spy; Mackiernan's collection of atomic intelligence about the Soviet Union's first atomic bomb (tested just across the border at the Semipalatinsk Test Site in Kazakhstan) was first revealed by the journalist Thomas Laird, but only confirmed by the CIA in 2008.
Emil Julius Klaus Fuchs (29 December 1911 – 28 January 1988) was a German theoretical physicist and atomic spy who, in 1950, was convicted of supplying information from the American, British, and Canadian Manhattan Project to the Soviet Union during and shortly after the Second World War.
 While at the Los Alamos National Laboratory, Fuchs was responsible for many significant theoretical calculations relating to the first nuclear weapons, and later, early models of the hydrogen bomb.
The IPCRESS File is Len Deighton's first spy novel, published in 1962.
 It was made into a film in 1965 produced by Harry Saltzman, directed by Sidney J. Furie and starring Michael Caine.
 The novel, which involves Cold War brainwashing, includes scenes in Lebanon and on an atoll for a United States atomic weapon test, as well as information about Joe One, the Soviet Union's first atomic bomb, although these elements did not appear in the film version.
David Greenglass (March 2, 1922 – July 1, 2014) was an atomic spy for the Soviet Union who worked on the Manhattan Project.
 He was briefly stationed at the Clinton Engineer Works uranium enrichment facility at Oak Ridge, Tennessee, and then worked at the Los Alamos laboratory in New Mexico from August 1944 until February 1946.
 He provided testimony that helped convict his sister and brother-in-law Ethel and Julius Rosenberg, who were executed for their spying activity.
 Greenglass served nine and a half years in prison.
Mark Strauss (born November 8, 1966) is a U.S. journalist.
 Previously, he was a senior editor at io9.com, covering politics and science, and a senior editor at "Smithsonian Magazine."
 Prior to that, he was the editor of the "Bulletin of the Atomic Scientists", winner of the 2007 National Magazine Award for General Excellence (in the under 100,000 circulation category), which was awarded by the American Society of Magazine Editors.
 Before joining the "Bulletin", Strauss was a senior editor at the bimonthly magazine "Foreign Policy", for which he had worked since 1997.
 He has contributed articles to "Slate", the "Chronicle of Higher Education", "The Washington Post", "The New Republic", "The Spectator", the "Brown Journal of World Affairs", and "Washington Monthly".
 He has also appeared as a commentator on CNN, Fox News, National Public Radio, and the BBC.
 Prior to joining "Foreign Policy", he was a research assistant at the Brookings Institution's Foreign Policy Studies program, and he served on the staff of a number of prominent national magazines, including "SAIS Review", "Spy Magazine", and "Discover Magazine".
Ruth Leah Greenglass (née Printz; April 30, 1924 – April 7, 2008) was an atomic spy for the Soviet Union along with her husband David Greenglass.