Morton Sobell, the co-defendant of Ethel and Julius Rosenberg in the 1951 spy trial, died the day after Christmas at the age of 101 but that only became a public story this week. After the Rosenbergs were arrested, Sobell fled with his family to Mexico, from where they hoped to go to one of the Soviet satellites in Eastern Europe. Before he could make contact, Mexican police officers arrested him and handed him over to U.S. federal agents. He served 18 years of a 30-year sentence and was released in 1969.

For decades, Sobell maintained his innocence, appearing at one forum after another, challenging those who claimed he was guilty. His response to the mounting evidence against him and Julius Rosenberg was to hurl invective at anyone who questioned their loyalty. His friend Max Elitcher’s sworn testimony that Sobell and Rosenberg had openly discussed their espionage activities was a lie, Sobell said. Decrypted KGB cables implicating Sobell and his comrades that came out with the first Venona release in 1995 had been either forged or grossly misinterpreted, he insisted. The effort of Julius Rosenberg’s handler, KGB agent Alexander Feklisov, to rehabilitate Sobell and the Rosenbergs as Soviet patriots were, Sobell maintained, slanderous ravings of a senile espionage chief.

When Feklisov’s son spoke on his father’s behalf at a New York City forum in the early 2000s, Sobell rose up from the audience and shouted that he and his father were liars. The young Feklisov answered by reminding Sobell that he had seen him in Moscow after his release from prison, that the KGB had put him and his wife up in luxurious accommodations and given his wife, Helen, a Russian mink coat.

I had a hint way back in 1978 that his denials were not exactly true. When I was beginning my research on the Rosenberg case, I phoned Sobell and requested that we set up a date for an in-person interview. He answered by asking me what more could be said about the Rosenberg case, since so much had already been written about it. After giving him a litany of unanswered questions, he stunned me when he replied: “Are you interested in the historical truth?” Of course, I replied. I’m a historian and that is precisely what historians do. He responded with an answer that I read as a blatant admission of guilt;

“At this time and juncture we’re living in,” he rhetorically asked, “do you think this is helpful? How will the historical truth hurt the establishment?” He added, “I’m a radical, not a liberal," and that at the present time “it is best that the historical truth not come out.”

Then in a stunning reversal, he told New York Times reporter Sam Roberts in 2008 that he was indeed guilty, and had stolen classified military documents for the Soviet Union. Yet, he argued that what he gave the Soviets did no harm to the United States. “What I did was simply defensive, an aircraft gun,” he said [to Sam Roberts]. “This was defensive. You cannot plead that what you did was only defensive stuff, but there’s a big difference between giving that and stuff that could be used to attack our country.” In effect, Sobell confessed to an ethical misdemeanor: passing along data of no consequence to an ally.

His story changed again in December 2010 when he talked to Steven Usdin for an article we were writing in The Weekly Standard. Only then did Sobell reveal that he had indeed been a key participant in an espionage operation that provided an enormous amount of classified data to the KGB, information that was extremely useful to the Soviet military. He acknowledged that a member of Rosenberg’s ring had broken into the safe in the office at Columbia University of Theodore von Karman, at the time the world’s most prominent aerospace engineer, and chairman of the U.S. Air Force Scientific Advisory Board. Von Karman was a man who shaped much of America’s postwar military strategy and who was trusted with some of the Pentagon’s most closely guarded secrets. In his safe were documents from Langley Field in Virginia, a preeminent center for military aviation design.

The Soviet agent who took the documents, scientist William Perl, then with others in Julius’ network, spent an entire weekend taking films with a Leica of the highly classified 1,885 pages, documents of extreme value to the Soviet Union. Perl returned them to the safe on Monday morning. One of the documents addressed the feasibility of nuclear-powered aircraft. The documents came to the Soviet Union precisely when Joseph Stalin was creating a crash program to improve Soviet military information.

He engaged in espionage, Sobell admitted to Usdin, for one reason only: “I did it for the Soviet Union.” To writer David Evanier, who was contemplating writing a biography of Sobell, he said simply “I bet on the wrong horse.” Sobell’s admission undermined the claims of the Rosenberg’s defenders that they were helping an ally and were motivated only by anti-fascist sentiment.

Sobell also admitted that he spied up until the Rosenbergs were arrested, at a time when the Cold War was well under way and Stalin’s Soviet Union was not an ally of the United States. In the five years between the end of the war and the unraveling of the Rosenberg spy ring, Sobell had access to a wealth of classified military material, including detailed information about the characteristics and capabilities of every American bomber, designs for analogue and digital computers used to automate antiaircraft weapons, and specifications for land-based and airborne radars that were later deployed in Korea. Indeed, during the Korean War, High Air Force and NACA officials told the New York World-Telegram on July 9, 1953, that data stolen by Perl [from Von Karman’s safe] were probably used in the design of the Russian high-tailed MiG fighter jet that was deployed in Korea against American airmen. So much for Sobell’s claim that the spying he engaged in did no harm to the United States.

Yet even today, leftist defenders of the Rosenbergs and Sobell still argue that even if they were guilty, they helped America’s Soviet allies when the Russians most needed it and that they did no harm to their country. Indeed, on Friday the Rosenberg’s sons, Michael and Robert Meeropol, released a statement emphasizing what they thought Sobell’s legacy was.

Sobell, they write, had only stolen “non-atomic military and industrial information,” as if that made his betrayal seem less important than had he handed over atomic bomb secrets. What is important is that they did not name names. As they write, “Mort stood in solidarity with Ethel and Julius at their darkest hour, at great personal cost.” One has to pause to remember that Sobell and the Rosenbergs were not arrested and put on trial for anti-war beliefs (as the left claimed at the time), but because they were spies for Joe Stalin. Sobell’s passing, they wrote, makes us reflect “on the notion of solidarity, and on the sacrifices people are willing to make for their most deeply held values and beliefs.”

Finally, they conclude that Sobell’s passing makes us think “about how our government’s playbook of fearmongering and repression—so much a part of the Morton Sobell and Ethel and Julius Rosenberg—is once again being embraced and utilized by those in power in our country today.”

Sadly, the “deeply held values” they believed in were to aid the power of an oppressive system led by one of the world’s greatest tyrants.