To unearth the truth about anyone’s life requires extensive research into the motives, desires, fears, beliefs, and hopes that drive decisions and accomplishments. Buried in letters, journals, postcards, news clips, yearbooks, photos, maps, tax records, ship manifests, passports, even inscriptions in books, such details are not always easy to find. And telling the story of a spy is doubly difficult because the main players in the narrative have used their expertise to block all potential paths to the truth, during their lifetimes and ad infinitum. In researching the biography of George Koval, there was the added complication that he was a spy for the GRU (Soviet military intelligence), whose records for work in America during the 1940s are still largely inaccessible.

As I noted in the epilogue of this book, only a small percentage of decrypted wartime cables sent to and from Soviet spies in America revealed GRU operatives. “We knew next to nothing about the extent of the GRU’s espionage operation against the Manhattan Project until the Koval thing came up,” said Cold War expert John Earl Haynes, in 2007, also a prolific writer on the US counterintelligence project—code name Venona—to decipher the Soviet spy exchanges. And as Soviet intelligence historian Jonathan Haslam wrote in his 2019 book Near and Distant Neighbors, the history of the GRU “has yet to reach the public eye.”

So how to research the life of an undetected GRU atomic spy in America in the 1940s? Proceed with the wisdom that the story of Soviet espionage in the West during World War II is in the early stages of discovery. And accept that there will be unanswered questions. Then, move forward with extensive, resolute goals to explore primary sources and records, seek FBI case reports, compile detailed chronologies of the narrative’s major players, chart the addresses of cover shops and residences, disprove coincidences, and study the excellent books and articles by espionage experts thus far.

For Sleeper Agent, the far-reaching FBI case files of George Koval, Benjamin Lassen, and Arthur Adams—also several hundred pages of the Nathan Gregory Silvermaster reports and a multitude of J. Edgar Hoover memos—were immensely helpful, especially regarding interviews with people across a vast landscape of former colleagues, bosses, employees, landlords, classmates, girlfriends, relatives, and teachers. There were also the FBI agents’ thorough surveys of official documents, such as passport applications, army registrations, security files, and legal records of all sorts. Sifting through the nearly seven thousand pages of reports did indeed lead to significant primary sources as well as links for the chronologies and descriptions of major players in the narrative. However, it must be said that the files do contain contradictions and occasional errors as well as repetitions and redactions. Facts often must be double-checked.

I also consulted exceptional secondary sources, as listed in the selected bibliography, ones with research notes almost as stimulating as the texts and worthy perhaps of a future book revealing the best methods and resources for extensive research into wartime Soviet espionage in America. And, as noted in the acknowledgments, I sorted through many documents in archival collections nationwide.

My quest was to get as close to the truth as possible, of course, and to answer at least a few of the long-lingering questions about Koval’s GRU “business trip” in America. For example, the narrative  shows that it was not sheer luck that Koval ended up at the Oak Ridge site of the Manhattan Project in August 1944. Also, Koval’s difficulties after returning to Moscow in 1948 had nothing to do with a failed mission, and his known reports to Soviet intelligence in Moscow regarding the Oak Ridge site, the polonium production, and the radiation safety efforts helped to shorten the Soviets’ project to build their first atomic bomb. But there is the frustration of unanswered questions. How many reports did Koval send to Soviet military intelligence and exactly when? Were Koval’s postcard recipients in 1948 connected to his espionage work, or at least aware of his double life? Was the courier “Clyde” another code name for Benjamin Lassen? And who didn’t meet Koval at the Grand Central Palace in September 1948? This is the type of book that prompts obsession. But there must always be a stopping point.

My hope is twofold: that Sleeper Agent will deepen the reader’s understanding of the intriguing psychology of a spy and of the timeless cost of oppression; and that it will be helpful to future researchers by contributing to the step-by-step process of prying open the closed chapters in the story of Soviet espionage in America.