In May 1957, a Finnish man named Reino Häyhänen walked into the United States embassy in Paris. He was there to surrender himself and, ultimately, request amnesty. He was on his way to Moscow but did not want to go there. He claimed he was a Soviet spy and that he was being recalled to the Soviet Union—but he wanted to go back to America, where he had worked as a KGB agent for the previous five years. After U.S. authorities spent a few days checking into his story, he was sent back to the United States. On May 10, 1957, he arrived in New York where he underwent an intense examination by the FBI.
After verifying Häyhänen’s identity, the FBI looked to him to solve a puzzle that had been befuddling the agency for four years. According to the Bureau’s website (which has a collection of “famous cases and criminals”), one day a newspaper delivery boy discovered a strange-feeling nickel during the course of his daily business. When he dropped it on the ground, the nickel split open. It was hollow. Inside it was a tiny photograph of a list of five-digit numbers. The paperboy, suspecting something fishy (this was the height of the Cold War, after all), brought the coin to the Feds.
The Bureau was baffled. Hollow coins were commonly used by illusionists, but this one was different from anything the FBI or novelty shop owners had seen before. The coin was made from opposite sides of two real coins, somehow connected together. There was a pin-sized hole in front, which the intended recipient could use to pop the halves apart, but the hole was designed to avoid detection and would not have allowed an illusionist easy access to the item held within. Besides, one novelty store shopkeeper told agents, the hollowed-out area was too small for any magic trick. This seemed to be an encoded message, and the intended recipient wasn’t the paperboy.
The good news for the FBI? The Bureau, with information given to them by Häyhänen, was able to decode the message. Unfortunately, it wasn’t very helpful. It was a letter from the KGB to a Soviet spy who was placed in New York, welcoming him to the United States and explaining some early details of his mission, including where he could get some money to start a new life in America. But it did not help the FBI identify who wrote the note nor its intended recipient.
As it turned out, the G-men didn’t have to. Upon further investigation, the FBI declared that it not only knew who the intended recipient was, but it also knew exactly where to find him. In a strange coincidence, the note was intended for Häyhänen himself.
With Häyhänen’s continued assistance, the FBI identified a Soviet spy named Rudolf Ivanovich Abel still living in the States. Abel was sentenced to thirty-five years in prison and was ultimately shipped back to Russia in 1962, in exchange for an American pilot who was being held as a prisoner of war.
Over a two-week period in 2010, U.S. authorities arrested ten Russian spies. After about ten days, the spies were sent back to Russia in exchange for Americans captured abroad. Why didn’t the FBI prosecute instead? According to Slate, doing so would require the FBI to disclose, to the courts and therefore the public, the tactics used by these spies. In doing so, the Russian spy agency would know which tactics were no longer viable, and could adjust accordingly. Returning the spies allows the FBI to maintain the secrets to its secrets.