After his arrest and interrogation, Weiss proved to be remarkably cooperative, and in return for a confession he was promised immunity by MI5.
[4] He was found to have been a key individual in Soviet intelligence in the United Kingdom during the interwar period but had ceased working as an agent in 1941.
[6] While at university, he joined the Communist Party of Germany (KPD)[1] While in Frankfurt in May or June 1931, Weiss was contacted by Hans Demetz who offered him a job, if he was interested in travelling overseas for work.
[8] After Weiss graduated he worked as a manager or buyer in a number of retail stores in Frankfurt and later in Cologne.
[13] By July 1936, he was working as the assistant editor and article author on the Railway Gazette and the South African Journal of Economics.
[6] In 1936, Weiss received intelligence detailing the production of aeroplanes from two of his most important informants, "Vernon" and "Meredith"[12] and was known to them under the alias of Walter Lock.
[16] In November 1936, Harry II introduced the Belgian communist Germaine Schneider to Weiss in South Kensington, London.
[17] Schneider was the groups courier from 1936 to 1939, meeting Weiss at a hotel in South Kensington several more times to exchange intelligence.
[4] Michael Friend Serpell, a career MI5 officer who was an expert on Soviet espionage, and another career MI5 officer, Robert Hembleys-Scales, undertook a detailed analysis of the papers and in the process discovered the existence of a Soviet GRU espionage network in the UK, and identified some of the spies that worked with Weiss.
[4] When the report was published, the task of finding Weiss and the other agents was assigned to case officer Roger Hollis.
[4] On 26 March 1947, Hollis said, "we are most anxious to avoid any chance of alarming Weiss and therefore, prefer the telephone check to other methods in this case".
[24] MI5 Director-General Percy Sillitoe had informed the prime minister Clement Attlee, due to what they considered the sensitive nature of the case.