A native of Germany, William Sebold served in the German army during World War I. After leaving Germany in 1921, he worked in industrial and aircraft plants throughout the United States and South America. On February 10, 1936, he became a naturalized citizen of the United States.

Sebold returned to Germany in February, 1939, to visit his mother in Mulheim. Upon his arrival in Hamburg, Germany, he was approached by a member of the Gestapo who said that Sebold would be contacted in the near future. Sebold proceeded to Mulheim where he obtained employment.

In September, 1939, a Dr. Gassner visited Sebold in Mulheim and interrogated him regarding military planes and equipment in the United States. He also asked Sebold to return to the United States as an espionage agent for Germany. Subsequent visits by Dr. Gassner and a "Dr. Renken," later identified as Major Nickolaus Ritter of the German Secret Service, persuaded Sebold to cooperate with the Reich because he feared reprisals against family members still living in Germany.

Since Sebold's passport has been stolen shortly after his first visit from Dr. Gassner, Sebold went to the American Consulate in Cologne, Germany, to obtain a new one. While doing so, Sebold secretly told personnel of the American Consulate about his future role as a German agent and expressed his wish to cooperate with the FBI upon his return to America. Sebold reported to Hamburg, Germany, where he was instructed in such areas as preparing coded messages and microphotographs. Upon completion of training, he was given five microphotographs containing instructions for preparing a code and detailing the type of information he was to transmit to Germany from the United States. Sebold was told to retain two of the microphotographs and to deliver the other three to German operatives in the United States. After receiving final instructions, including using the assumed name of "Harry Sawyer," he sailed from Genoa, Italy, and arrived in New York City on February 8, 1940.

The FBI previously had been advised of Sebold's expected arrival, his mission, and his intentions to assist them in identifying German agents in the United States. Under the guidance of Special Agents, Sebold established residence in New York City as Harry Sawyer. Also, an office was established for him as a consultant diesel engineer, to be used as a cover in establishing contacts with members of the spy ring. In selecting the office for Sebold, FBI Agents ensured that they could observe any meetings taking place there.

In May, 1940, a shortwave radio-transmitting station operated by FBI Agents on Long Island established contact with the German Shortwave station abroad. This radio station served as a main channel of communication between German spies in New York City and their superiors in Germany for 16 months. During this time, the FBI's radio station transmitted over 300 messages to Germany, and received 200 messages from Germany.

Sebold's success as a counterespionage agent against Nazi spies in the United States is demonstrated by the successful prosecution of the 33 German agents in New York. Of those arrested on the charge of espionage, 19 pleaded guilty. The 14 men who entered pleas of not guilty were brought to trial in Federal District Court, Brooklyn, New York, on September 3, 1941; and they were all found guilty by jury of December 13, 1941.

Click on the members photo for more information on the activities of each of these convicted spies and Sebold's role in uncovering their espionage activities for the Reich.