After the FBI obtained the nickel and the microfilm, they tried to find out where the nickel had come from and what the numbers meant. The nickel had a 1948 front, but because of the copper-silver alloys used the back was from 1942 to 1945. There were five digits together in each number, 21 sets of five in seven columns and another 20 in three columns, making a total of 207 sets of five digits. There was no key for the numbers. The FBI tried for nearly four years to find the origin of the nickel and the meaning of the numbers.
But it wasn't until a KGB agent, Reino Häyhänen (aka Eugene Nicolai Mäki), wanted to defect in May, 1957, from Paris, was the FBI be able to link the nickel to KGB agents, including Mikhail Nikolaevich Svirin (an ex-United Nations employee) and Vilyam Genrikhovich Fisher. Häyhänen was being recalled to Moscow for good, and defected on the way back in Paris. The deciphered message in the nickel turned out to be worthless, a personal message to Häyhänen from the KGB in Moscow welcoming him to the U.S. and instructing him on getting set up. He would give the FBI the information that it needed to crack the cipher, uncover the identity of his two main contacts in New York (Svirin and Fisher), and a nearly identically made Finnish 50 Markka coin.
In addition to Svirin and Fisher (code name "Mark"), Häyhänen (code name "Vic") told the FBI about Vitali G. Pavlov, onetime Soviet embassy official in Ottawa; Aleksandr Mikhailovich Korotkov; and U.S. Army Sergeant, Roy Rhodes (code name "Quebec"), who had once worked in the garage of the U.S. embassy in Moscow. The KGB was able to get to Rhodes because it had "compromising materials" about him. Häyhänen and Fisher were in the United States mainly looking for information on the U.S. atomic program and U.S. Navy submarine information.
Svirin had returned to the Soviet Union in October, 1956, so was not available for questioning or arrest.
When Fisher was arrested, the hotel room and photo studio that he lived in contained multiple modern espionage equipment items: cameras and film for producing microdots, cipher pads, cuff links, hollow shaving brush, shortwave radios, and numerous "trick" containers.
Fisher was brought to trial in New York City Federal Court, indicted as a Russian spy, in October, 1957, on three counts:
Häyhänen testified against Fisher at the trial.
On October 25, 1957, the jury found Fisher guilty on all three counts. Judge Mortimer W. Byers sentenced him, sentences to be served concurrently, on November 15, 1957, count one: 30 years' imprisonment; count two: 10 years' imprisonment and $2,000 fine; count three: 5 years' imprisonment and $1,000 fine.