Yatskov gave details about Perseus' recruitment, how he sent information from New Mexico to New York (through Morris Cohen's wife), and confirmed that the Soviet Union received information from both, Klaus Fuchs and Perseus.
In an interview given before his death in 1995, the American-born Soviet spy Morris Cohen confirmed that in addition to Karl Fuchs, there was a second physicist in the Manhattan project who worked as a Soviet spy.
The details in Cohen's story coincide with the statements of Colonel Vladimir Chikov a few years ago, such as the recruitment of people close to the Manhattan Project as spies, the existence (suspected by the American intelligence) of an unidentified scientist who collaborated with Soviet intelligence, and the interaction of said scientist with Lona Cohen (Morris Cohen's wife) to transport stolen information.
According to Cohen, by the fall of 1994 there were very few people left in Soviet intelligence ("two or maybe three") who knew the real name of the second spy scientist.
For her part, shortly before her death in 1992, Lona Cohen had a telephone interview with historian Walter Schneir. In that interview, Lona Cohen confirmed that she had made at least one trip between Albuquerque and New York to transport classified information stolen to the United States, but she could not quite remember who she had interviewed with in New Mexico, saying that it was probably a scientist or physicist.
The Venona project was a United States counterintelligence program run by the Signal Intelligence Service that (later became part of the National Security Agency,) started in the Second World War and was active since February 1943 to October 1980.
The objective of the program was to intercept and decrypt messages from diplomats, intelligence agencies (such as the NKVD and the KGB), business representatives and other actors of the Soviet government.
Despite the fact that only a fraction of the messages intercepted by Venona were suitable for decryption, the project left an archive of around 3000 decrypted and translated messages.
Although there is no mention of Perseus in the Venona files, there are references to a spy under the code name PERS or FOGEL. Apparently, at some point the codename PERS was turned into Perseus by mistake.
PERS was identified in the Venona files as part of the group of four Soviet spies (of which only 3 had been identified) who infiltrated the Manhattan Project.
Despite the fact that by 2012 a publication by NSA's Center for Cryptologic History described PERS as ""important, but still unidentified"", the references in the Venona files have been questioned or even used to confirm that Perseus never existed.
From the early 1950s till 1995, three Soviet spies had been confirmed to have infiltrated Los Alamos: Klaus Fuchs (German physicist), David Greenglass (military man and brother-in-law of Julius Rosenberg) and Theodore Hall (American physicist).
Fuchs voluntarily confessed to British MI5 authorities in January 1950 and this subsequently lead to Greenglass in June of that same year. Finally, Hall's involvement was not identified until the release of documents from Venona in 1995, a few years before his death in 1999.
After the dissolution of the Soviet Union, publications like those by Chikov and Yatskov strengthened the theory of a possible fourth spy in Los Alamos, who would have been identified as Perseus (the PERS in the Venona files) or FOGEL.
In 1994 the lieutenant general and Soviet agent Pavel Sudoplatov published a book titled "Special Tasks".
In the book, Sudoplatov referred to the statements made by Anatoly Yatskov, and stated that he did not remember that code name and, that in his opinion, it could be that Yatskov or his associates created Perseus to cover the true identities of Soviet informants.
However, Sudoplatov also acknowledged that the codename Perseus was used to refer to or cover a number agents and anonymous sources.
United States Cold War historian John Earl Haynes concluded that Perseus was an invention relying on the research of authors Joseph Albright, Marcia Kunstel and Gary Kern.
In an index of false names, pseudonyms, and real names of spies, Haynes notes under the Perseus entry that:
However, Haynes acknowledges that although Perseus was an invention, there must have been a 4th Soviet spy operating in Los Alamos during the development of the Manhattan project in addition to the 3 spies identified until 1995: Klaus Fuchs, David Greenglass and Theodore Hall.
In their book "Bombshell: The Secret Story of America's Unknown Atomic Spy Conspiracy", the authors Joseph Albright and Marcia Kunstel dedicate the twentieth chapter to Perseus under the title of "The Perseus Myth" in which they conclude that the spy never existed.
According to the authors, the KGB may have created Perseus for the purposes of self-promotion, justify its own existence, and even to secure more state funding.
In 2006 mail that was made public, author Gary Kern explained why he believed Perseus was an invention. Kern believes that Perseus was an extremely risky disinformation operation with multiple objectives, including:
In April 1999 American scientist, activist and, president of the Federation of American Scientists from 1970 to 2000; Jeremy Stone, published his memoirs under the title «"Every Man Should Try": Adventures of a Public Interest Activist"».
Motivated by an article in The Washington Post about Vladimir Chikov's publications in Russia, Stone decided to take on the subject, and in his book he disclosed conversations and visits he had with someone he knew personally and only identified with the pseudonym "Scientist X" (or «Dr. X» ), and explained why he believed that this "Scientist X" was the real Perseus.
Despite the use of a pseudonym, thanks to the information in the book, the "Scientist X" was easily identified as Philip Morrison, a physicist from the Massachusetts Institute of Technology.
Morrison denied the accusation and gave a solid rebuttal against it, noting that:
On the other hand, the reasons that led Stone to suspect Morrison were questioned. Namely, those reasons included:
To all of the above, Stone accepted Morrison's rebuttal, stating that: "In the light of these facts, which I certainly cannot contradict, [...] I can only accept your denial that you are Perseus."
Finally, thanks to the controversy raised by the event, several academics and people close to the Federation of American Scientists expressed their wishes for Stone to apologize, and even the idea of calling Stone to present his resignation as head of the Federation.
According to historian John Earl Haynes and academic Harvey Klehr, thanks to FBI documents that were declassified in the 2010s, they were able to confirm the existence of a suspected fourth spy who they identified as Oscar Seborer.
Seborer was an American engineer who was drafted into the United States Army in 1942 and, like all his siblings, had sympathy for the Communist Party USA.
Given his education as an engineer, Seborer was assigned to the «Special Engineer Detachment», a program that identified members of the military with specific abilities and funneled them to the Manhattan project.
However, Haynes and Klehr are emphatic that Seborer should not be identified with Perseus, since while Perseus would have been an invention probably based on Theodore Hall, Seborer's life and profile have no relation to the characteristics attributed to Perseus.
According to historian John Eark Haynes and academic Harvey Klehr, although Perseus never really existed, some aspects of his character were based on or coincide with the American Soviet spy and physicist Theodore Hall. These aspects include:
Born in New York City, Hall was an American physicist who was considered a prodigy from an early age and graduate from Harvard University at 18. Concerned about the advance of fascism at the time, Hall developed sympathies for socialism.