RUTHFULLY YOURS

The most infamous chapter was the atomic espionage case of Ethel and Julius Rosenberg, who were convicted of espionage and executed in June 1953. Even at the time, many people didn’t know there was a third defendant tried with the Rosenbergs. His name was Morton Sobell ; he was convicted and imprisoned for conspiracy to commit espionage. Born half a year before the October Revolution, he is still alive at 101.

I first visited him at his Manhattan apartment in 1982. He had freedom, girlfriends, a Social Security check. My early interviews with him hinted at how much he wanted to let the world know he had been a great spy—but he was torn. Was he a martyr who had helped the Soviets, or a scapegoat for the U.S. government? There was a tension between wanting to do the right thing for the U.S.S.R. by proclaiming his innocence and his egotistical need for attention by making his crimes known.

Julius Rosenberg recruited Mr. Sobell in December 1943 to spy for the Soviet Union. In June 1947, Mr. Sobell was hired by the Reeves Instrument Corp., which was working on ballistic-missile defense systems. The classified information he gave the Soviet Union was later used against America in both Korea and Vietnam.

Mr. Sobell recalled that, on a frantic weekend in 1948, he helped copy hundreds of pages of secret Air Force documents stolen from the safe of Theodore von Karman, a world-renowned aerospace engineer. The material included data about the Lexington report, a study of the feasibility of nuclear-powered aircraft. Mr. Sobell, Julius Rosenberg, William Perl and an unidentified fourth man spent a weekend on Morton Street in Greenwich Village, photographing all of von Karman’s files. Mr. Sobell described that weekend to me as wild, exciting and “fun.”

When the Rosenbergs were about to be arrested in 1950, Mr. Sobell fled to Mexico. Once he got there, he used many aliases and looked frantically for passage to the Soviet Union. Yet when he visited the Soviet Embassy in Mexico City, he never asked for help. Mexican authorities arrested Mr. Sobell—he tried to grab a gun from them—and delivered him to the U.S. to face trial with the Rosenbergs.

He was sentenced to 30 years and served almost 18. On his release in 1969, he went to Moscow and received a hero’s welcome from the KGB. His handler, Alexander Feklisov, revealed in a memoir that Mr. Sobell passed on thousands of pages of text and drawings of valuable military secrets about sonar, radar, infrared rays and the aiming devices for artillery pieces, along with the first data on missile-guidance systems that could be used for the atomic bomb.

In 2008, after 58 years of noisily asserting that he had been framed, Mr. Sobell astonished his supporters by telling a reporter that he had, in fact, been guilty of spying for the Soviet Union. I had already written about him in my novel about the Rosenberg case, “Red Love.” But in 2011 his stepdaughter, Kate Riley, approached me about writing his biography.

And so Morton Sobell and I sat facing each other again after 29 years. Though he admitted what he’d done, he was unrepentant. “I bet on the wrong horse!” he quipped when I asked why he’d betrayed America. “I thought the U.S.S.R. was a genuine socialist country and this was the ideal.”

I asked him if spying for the Soviet Union was part of being progressive.

“To me, it was natural, yes,” he replied. “But the U.S.S.R. was the biggest disillusionment. Capitalism has its points. It’s dynamic! Theirs was very static. They didn’t understand the dynamics of growth.”

But there was the monstrous terror, too.

Without batting an eyelash: “Well, that comes with the territory.”

Mr. Sobell introduced me as his “inquisitor” to his grandson Max Sobell. The young Mr. Sobell bantered with the elder. Morton Sobell can be a charmer, like many of the psychopaths I have known.

Max Sobell reminded him: “You still had the camera in Mexico that you photographed secrets with.”

“Yeah,” Sobell shouted, “the Mexican police stole it!”

“No, it’s evidence,” Max said.

“They didn’t know that.”

Max: “ ‘I had this great Colt 45 and I killed someone . . . and they stole my gun!’ See the point?”

“No,” Morton Sobell said. “And they paid the Mexican police to kidnap me. That’s crooked.”

“So institutions still have to play by the rules, but individuals don’t? Your alias was Morton Sand. You were being deceitful.”

“Ohhhhh! You have a lot to learn, my boy!”

Trying to clear this up, I said to Morton Sobell, “But you stole the secrets, right?”

“Stole?” he replied. “I transmitted them.”

He paused, then asked: “Are you going to publish this in a high-end publication?”

Mr. Evanier is author of 10 books, including “Woody: The Biography,” and a former senior editor of the Paris Review. His forthcoming biography is tentatively titled “Rogue Spy: The Life of Morton Sobell.”