Ted Hall was 16 years old when in 1944 he was recruited as the youngest physicist for the Manhattan Project, the top-secret U.S. program to develop the world’s first nuclear bomb. An idealist and pacifist, Hall did not share the enthusiasm of his colleagues after the successful explosion of the world’s first atomic bomb in Los Alamos. He became increasingly concerned that a U.S. post-war monopoly on such powerful weapons could lead to a nuclear catastrophe. After discussions with his Harvard colleague and roommate, Saville Sax, both decided to pass key information about the implosion bomb to the Soviet Union.

In 1947 Hall met the woman he wanted to marry, but he insisted on revealing the explosive secret of his espionage to her before they took their vows.  The couple started a family while Hall refocused his scientific talents on pioneering research in biophysics. The FBI kept the family under surveillance for many years, but never charged Hall with a crime. Hall’s wife Joan kept her husband’s secret for over 50 years, until his death in 1999.

“A Compassionate Spy,” a documentary by two-time Oscar-nominated Steve James, reveals the twists and turns of this little-known true story, as well as its profound impact on nuclear history. We spoke to James in an exclusive interview after the film premiere at the Venice Film Festival.

Why were you drawn to the story?

I didn’t know anything about Ted Hall until I met a journalist Dave Lindorff, who often reports on nuclear weapon issues and who is also one of the producers of our film. He told me about Joan and the extraordinary story about her husband. The scientist was a Harvard undergraduate, and at an incredibly young age he made a huge decision to pass secrets to the Soviets. Other spies eventually broke and confessed, and that is how they got arrested. But Ted was extremely careful. He and Joan kept this secret even from their children for most of their lives. I also learned of the existence of interviews with Ted, filmed by Dave, towards the end of Ted’s life, most of which had never been seen publicly. So there was this great opportunity to tell his story and to have his voice well-represented in the film.

Do you think Ted was a spy? If you did, why did you soften the word with “compassionate” in the title?

We struggled with the film title for a very long time. Joan, who was still alive, was against such a definition for her husband. Although Ted did not work for the Soviets or receive any benefits from them, his actions fit the definition of a spy. We tried to give this concept a different meaning, clarifying that being a spy does not automatically mean that he is doing something wrong.

I think by watching the film some people will conclude that Ted did wrong, especially since his fears that the US would turn radical in the post-war period or launch a preemptive strike against the Soviet Union were not justified. Others may think Ted overreacted, that he should not have passed the secrets. I think Ted was courageous. To me, it’s undisputable why he did it. He did it for the right reason, not to gain profit or fame. He did it because he had a genuine fear of what the U.S. was capable of. In his mind, this was not a matter of helping the Soviet Union, but rather a question of preventing an overall holocaust which would affect the entire world.

So you understand people who betray their country?

If Ted had been found out, he would not have even been charged with treason because of the U.S. status with the Soviets — at the time they were allies. You can only be charged with treason against the enemy of your country. So, to pass secrets to allies was espionage and illegal, but not treason.

The U.S. came very close to using the atomic bomb during the Korean War, and twice in Vietnam. The only thing that stopped them was that the Russians could retaliate. So you would have to say that Ted really did something heroic.

Did Ted continue his relationship with Soviet Union?

Ted said that he did not. However, he still was in touch with an agent in case of trouble if they needed to reach him.

Why are we still talking about nuclear war?

When a book [about Hall] came out in the end of 1990s, Ted and his actions were regarded with sympathy. I am interested to see what kind of conversations will be generated when my film is released, especially since there is the war going on in Ukraine. Now Russia does not have many adherents, and the fact that Putin threatened to use nuclear weapons has greatly alarmed the world. The message is out there. So, I think people will look at Ted’s actions from a contemporary stance. That’s what the film is trying to do — to make you look at recent events through the lens of the time when he was living.

This interview has been edited for length and clarity.