The Morton Sobell, who was tried and convicted with Ethel and Julius Rosenberg of espionage and has now confessed at the age of 91, turns out to be the same insouciant Morty I remember from the mid-1980s when I was interviewing and pestering him while writing my novel about the Rosenberg case, “Red Love.” “Yeah, yeah, yeah, call it that,” he says now, in an interview with Sam Roberts of the New York Times, about his spying for the Soviet Union. His confession was no surprise; he almost confessed to me more than 20 years ago.

As a boy, I had pondered the posters of the Rosenbergs with Morton looking over their shoulders. I began to hang around the bizarre Communist Party milieu, trying to figure it out and in search of a girl friend and a family. The party lived and breathed the Soviet Union. At the rallies before and after the execution, the people around me had wept and shouted the innocence of the Rosenbergs and Sobell. In 1985 I began writing my novel.

In those days Sobell was living on West 109th Street off Broadway on the Upper West Side. He was so happy to be free. He had social security; he had girls. “Whoo!” he told me. “I’ve got two girl friends.” Sweetness was Morty, and how he hated that part of himself. He had spent 19 years in Alcatraz, and he feared my compassion. I reminded him of himself. “I don’t go by the heart,” he said. “The heart betrays. I know that by the heart you can get a Nazi as easily as a Communist.”

He didn’t literally confess to me. But between long silences, he said something that haunted me. The topic was Julius Rosenberg. “I never had a good hold on him,” he said.

“Did you like him?” I asked.

Morton was silent for a long time. Then he looked down. “He was a comrade. This to me is saying a good deal. To understand what this meant is a whole story in itself.” That sentence and the next would hang in the air until this year, when he finished them.

I tried again. “What’s the story?”

“My friend,” he said, looking down again, “beyond that, you’ll have to use your imagination.”

I did, and was certain — as a novelist, not a historian — that he was guilty.

On my next visit, Morton was upset. “I haven’t been sleeping well since I last saw you,” he said. A few minutes later, he said, “You know, I can’t get deeply involved with a ‘personal’ person.”

“I guess that’s me,” I said.

“You’re an effete aesthete,” he snapped. “I’m the radical, you’re the liberal.”

He picked up a pamphlet. “Ever see this?” he said. It was the book of poems his wife Helen had published and dedicated to him while he was in prison.

“No, I haven’t,” I said.

“Two of the poems were to me. The others were to other guys. This wasn’t generally known at the time.”

“It must have hurt you,” I said. Morton stiffened.

“That was our relationship. I was powerless. Under the circumstances any other way would have seemed more painful.”

Morton struck his hand against the chair. “If it hurt me, it was my own fault. It’s because I’m too damn bourgeois.”

“Did it hurt you?”

“Of course it hurt me.” Morton took a framed picture of himself as a boy in Brooklyn, sitting on his father’s lap. He handed it to me. Then he took it back and placed it on the table.

“You don’t know where I’m coming from,” he said after a silence. “You’re too full of feeling — that’s what I get from you,” he said with contempt.

“No one’s more full of feeling than you.”

“But I control it.” Morton stood up. ” I think that’s it for today.”

He ripped my name off his bulletin board.

“Farfallen,” he said in Yiddish.

“What does that mean?”

“The opportunity is lost,” Morton Sobell said. It was the last time I saw him.

Now I no longer have to use my imagination.

Mr. Evanier is the author of “Red Love,” “The One-Star Jew,” and “The Great Kisser,” and a recipient of the Aga Khan Fiction Prize.