William G. Sebold

Before leaving Germany, Sebold visited the U.S. Consulate in Cologne, Germany, and insisted on speaking with the Consul General. He told the Consul that he had been blackmailed into becoming a German spy but that he was a loyal American citizen and wanted to cooperate with the Federal Bureau of Investigation (FBI) in the United States. The U.S. government agreed.[2][7]

Sebold sailed from Genoa, Italy, and arrived in New York City on February 8, 1940. There, Sebold (with secret help from the FBI) set himself up as a consulting diesel engineer, with an office in Times Square in Manhattan.[2][6]

With the assistance of the FBI, "Harry Sawyer" was able to obtain an office in Times Square for a company under the name "Diesel Research Company". This office provided a seemingly safe space where Nazi spies felt comfortable meeting with and discussing their plans with Sebold. The office also allowed spies to send letters to manufacturers like Consolidated Aircraft Corporation, where they would then receive letters back such as "Development of Diesel Engines."[8] The spies came to the office to deliver blueprints, wartime information, and other sensitive information regarding the United States. However, the office was outfitted with hidden microphones and two-way mirrors, so FBI agents would be able to film the meetings for future use. Using the office, the FBI were able to obtain countless hours of incriminating footage. For example, the group's leader Fritz Joubert Duquesne was caught discussing how fires could be started at industrial plants to slow production, and showed photographs of blueprints for a new bomb being built in the United States. In different footage, a spy explains his plan to bomb a building, going as far as bringing dynamite and detonation caps to Sebold's office.

Mugshots of Duquesne Spy Ring members. In his office and with cameras secretly rolling, Sebold met with a string of Nazis who wished to pass secret and sensitive national defense and wartime information to the Gestapo.[6]

Sebold was instructed by the Abwehr to contact Fritz Joubert Duquesne, code-named DUNN, a German spy in New York. Duquesne had been a spy for Germany since World War I; before that, he had been a Boer spy in the Second Boer War.[5][9] In the United States, Duquesne had been a New York Herald journalist and was the "master coordinator" of the Nazi spies operating in the United States. He contacted aircraft and other technology companies and requested information that he claimed he would use for his lectures. Any plans or photos that he received were sent to the Wehrmacht.

At their first meeting, Duquesne was extremely worried about the possibility of listening devices in Sebold's office. He gave Sebold a note suggesting that they should talk elsewhere. After relocating to an automat, the two men exchanged information about members of the German espionage system with whom they had been in contact.[2]

In his office and with cameras secretly rolling, Sebold met with a string of Nazis who wished to pass secret and sensitive national defense and wartime information to the Gestapo.[6]

Duquesne provided Sebold with information for transmittal to Germany during subsequent meetings, and the meetings which occurred in Sebold's office were filmed by FBI Agents. Duquesne, who was vehemently anti-British, submitted information dealing with national defense in America, the sailing of ships to British ports, and technology. He also regularly received money from Germany in payment for his services.[2]

On one occasion, Duquesne provided Sebold with photographs and specifications of a new type of bomb being produced in the United States. He claimed that he secured that material by secretly entering the DuPont plant in Wilmington, Delaware. Duquesne also explained how fires could be started in industrial plants. Much of the information Duquesne obtained was the result of his correspondence with industrial concerns. Representing himself as a student, he requested data concerning their products and manufacturing conditions.[2]

In May 1940, FBI agents on Long Island set up a shortwave radio station, and established contact with the Abwehr's radio station in Germany, posing as part of Sebold's spy ring. For 16 months this radio station was a main channel of communication between German spies in New York City and the Abwehr. During this time, the FBI's radio station transmitted over 300 messages containing falsified or useless information to Germany, and received 200 messages from Germany. Through Sebold, the U.S. identified dozens of German agents in the United States, Mexico and South America.[2][6]

In June 1941, the FBI arrested 33 German agents that were part of Sebold's network. Nineteen of the agents arrested pleaded guilty. The remainder were tried in Federal District Court, Brooklyn, New York, beginning 3 September 1941. The jury found all 14 guilty on 13 December 1941.[2] The 33 members of the Duquesne Spy Ring were sentenced to serve a total of over 300 years in prison. Duquesne was sentenced to 18 years in prison. The Duquesne Spy Ring remains the largest espionage case in U.S. history that ended in convictions.

As a result of the massive investigation, when the United States entered the war the FBI was confident that there was no major German espionage network hidden in U.S. society.[6]

When the trial ended, Sebold disappeared. He entered a government witness protection program and moved to California under another assumed identity. He had countless jobs, even trying to be a chicken farmer, but could never hold down a job and was constantly plagued by bad health. Additionally, letters from his family back in Germany explained that the Nazis still wanted to exact their revenge, leaving him in a constant state of fear. Sebold was diagnosed with manic depression and committed to Napa State Hospital in 1965. Five years later he suffered a heart attack and died.[5]