Editing Klaus Fuchs (section)

==Detection and confession==

By September 1949, information from the [[Venona project]] indicated to [[GCHQ]] that Fuchs was a spy,{{sfn|Goodman|2005|pp=126–128}} but the British intelligence services were wary of indicating the source of their information. The Soviets had broken off contact with him in February.{{sfn|Rhodes|1995|p=377}} Fuchs may have been subsequently tipped off by [[Kim Philby]]. After a great deal of research for his 2019 biography, ''Trinity'', Frank Close confirmed that while MI5 suspected Fuchs for over two years, "it was decrypters at GCHQ who supplied clear proof of his guilt ... not the crack American team that is normally given all the credit", according to a review of the book.<ref name="The Guardian">{{cite web |date=17 August 2019 |title=Trinity by Frank Close review – in pursuit of 'the spy of the century' |url=https://www.theguardian.com/books/2019/aug/17/trinity-by-frank-close-review-in-pursuit-of-the-spy-of-the-century |access-date=1 January 2021 |work=The Guardian |quote=Cleared by MI5, recruited by the Kremlin … the double life of a spy who helped develop the first atomic bomb}}</ref>

Under interrogation by [[MI5]] officer [[William Skardon]] at an informal meeting in December 1949, Fuchs initially denied being a spy and was not detained.{{sfn|Moss|1987|pp=134–136}} According to Nancy Thorndike Greenspan, author of a 2020 book, ''Atomic Spy: The Dark Lives of Klaus Fuchs'', Skardon told Fuchs that if he admitted his earlier espionage activity, he could be permitted to continue to work at Harwell.{{sfn|Greenspan|2020||pp=238-239}} In October 1949, Fuchs had approached Henry Arnold, the head of security at Harwell, with the news that his father had been given a chair at the [[University of Leipzig]] in [[East Germany]], and this information became a factor as well.{{sfn|Goodman|2005|pp=128–129}} In early January Fuchs was informed that he must resign his position at Harwell because of his father's appointment in East Germany. He was offered help in finding a university post.{{sfn|Greenspan|2020|p=249}}

Meeting with Skardon for a fourth time on 24 January 1950, Fuchs voluntarily confessed that he had shared information with the Soviets.{{sfn|Goodman|2005|pp=130–131}} According to Nancy Thorndike Greenspan, Skardon's report on their meeting "made no mention of his promise to Fuchs to stay on at Harwell if he confessed", but at the subsequent debriefing it was agreed "to maintain FUCHS in his present state of mind, and for this state of mind to be in no way disturbed". To make it possible to prosecute Fuchs, Skardon proposed that Fuchs be asked to prepare a  signed statement, which he then did at the War Office in London. The document included the statement "I was given the chance of admitting it and staying at Harwell or clearing out."{{sfn|Greenspan|2020|p=260-264}}

Three days later, he also directed a statement more technical in content to [[Michael Perrin]], the deputy controller of atomic energy within the Ministry of Supply.{{sfn|Williams|1987|pp=124–126}} Fuchs told interrogators that the NKGB had acquired an agent in [[Berkeley, California]], who had informed the Soviet Union about [[electromagnetic separation]] research of uranium-235 in 1942 or earlier.{{sfn|Rhodes|1995|pp=411–412}} Fuchs's statements to British and American intelligence agencies were used to implicate [[Harry Gold]],{{sfn|Rhodes|1995|pp=425–428}} a key witness in the trials of [[David Greenglass]] and [[Julius and Ethel Rosenberg]] in the United States.{{sfn|Rhodes|1995|pp=479–481}} Fuchs later stated that he passed detailed information on the project to the Soviet Union through courier Harry Gold in 1945, and further information about [[Edward Teller]]'s [[History of the Teller–Ulam design#Teller's "Super"|unworkable "Super" design]] for a [[hydrogen bomb]] in 1946 and 1947.{{sfn|Rhodes|1995|pp=244–246}} Fuchs also stated that "The last time when I handed over information [to Russian authorities] was in February or March 1949".<ref>{{cite web |url=https://www.nationalarchives.gov.uk/education/resources/cold-war-on-file/klaus-fuchs-confesses/ |title=Klaus Fuchs confesses, Transcript |date=30 May 2019 |work=The National Archives |access-date=1 January 2021 |quote= }}</ref><ref name="The Guardian" />

Fuchs was arrested on 2 February 1950, charged with violations of the Official Secrets Act. Nancy Thorndike Greenspan quotes from police notes on a visit between fellow scientist Peierls and Fuchs in detention shortly after the news of the arrest broke. When Peierls asked Fuchs why he had spied, Fuchs answered: "Knowledge of atomic research should not be the private property of any one country but should be shared with the rest of the world for the benefit of mankind."{{sfn|Greenspan|2020|p=276}}