The FBI spent years investigating J. Robert Oppenheimer, who helped make the WWII-ending atomic bomb. During the surveillance, interviewees alleged he was feeding nuclear secrets to the Soviet Union.

• The FBI spent years investigating J. Robert Oppenheimer, who helped make the WWII-ending atomic bomb.

• He was then tried by the Atomic Energy Commission, and his top-level security clearance was revoked.

• Reports from the FBI show Oppenheimer was accused of spreading information to the Soviets.

During an inquest into the actions of J. Robert Oppenheimer by the FBI, the agency investigated the "father of the atomic bomb" on suspicion of crimes including espionage and the dissemination of nuclear information to the Soviet Union.

As depicted in Christopher Nolan's summer blockbuster biopic "Oppenheimer," Oppenheimer's behavior came under renewed scrutiny in 1953 after William Borden, a staff director of the congressional Joint Committee on Atomic Energy, sent a letter to the FBI accusing Oppenheimer of being sympathetic to the Communist Party and possibly knowingly employing spies from the Soviet Union on his project developing the atomic bomb.

Borden's letter was most likely sent at the suggestion of Oppenheimer's political nemesis Lewis Strauss, a businessman turned member of the US Atomic Energy Commission.

While Oppenheimer's relationships and loyalties had been investigated prior to receiving his security clearance, efforts to discredit the physicist were redoubled by his rivals after he successfully led his team to create the atomic bomb, and the letter from Borden accelerated a chain of events that led to Oppenheimer losing his security clearance.

The renewed investigation into Oppenheimer's loyalties as his security clearance came up for renewal cited the letter's accusations, Oppenheimer's associations that the US government found suspicious, as well as a wiretap the FBI ordered on his phone —  now widely described as illegal — as evidence of his questionable loyalty to the United States.

Documents from the investigation include hundreds of pages of phone records, along with interviews with his colleagues.

Kenneth Pitzer, the dean of UC Berkeley's school of chemistry at the time, told agents in 1952 in an interview regarding the renewal of Oppenheimer's security clearance that his opinion of Oppenheimer had changed over the years — earlier, in 1947, he said he had "the utmost confidence in both the loyalty and the scientific ability" of Oppenheimer, according to FBI records.

During the investigation, though, Pitzer said he had new doubts about Oppenheimer's loyalty to the country because of Oppenheimer's initial reservations about the development of the hydrogen bomb, which some believed were an indication that he wanted the Soviet Union to develop the weapon first. Pitzer said Oppenheimer had "impeded" other scientists' progress on the bomb after his concerns were overruled.

Another professor, Ward Evans of Loyola University Chicago, said he felt Oppenheimer did not hinder the production of the H-bomb and said he was "less of a security risk than he was in 1947" when he was cleared by the Atomic Energy Commission over a separate matter, according to the investigation.

The other main accusation against Oppenheimer was that he might be a security risk over ties to communism. The scrutiny was fueled in part by his relationships with known communists like the psychiatrist Jean Tatlock, with whom Oppenheimer had a romantic relationship.

In FBI reporting, Oppenheimer was also linked to Bernard Peters, a graduate student of his who was at one time a member of the German Communist Party — these ties added to suspicions about Oppenheimer's objections to the H-bomb; critics attributed those objections to a loyalty to the Soviet Union rather than any conscientious objection over the development of the weapon.

The Atomic Heritage Foundation does consider Oppenheimer likely to have held communist sympathies, but it maintains that information in the FBI's report of its investigation was exaggerated. The AHF says it was "unclear" whether Oppenheimer ever formally joined the US Communist Party.

At the end of the inquest, despite no definitive proof that Oppenheimer was a Soviet spy or that he had employed spies in his work, Oppenheimer's top-level security clearances were revoked — a devastating blow to the scientist.

In 2022, US Energy Secretary Jennifer Granholm nullified the decision to revoke Oppenheimer's security clearance, saying in a statement that Oppenheimer had a "central role" in World War II and the Department of Energy had a "responsibility to correct the historical record and honor Dr. Oppenheimer's profound contributions to our national defense and the scientific enterprise at large."

"As time has passed, more evidence has come to light of the bias and unfairness of the process that Dr. Oppenheimer was subjected to," Granholm said in the statement. "While the evidence of his loyalty and love of country have only been further affirmed."

The FBI, the Department of Energy, and the Atomic Heritage Foundation didn't immediately respond to requests for comment.

Correction: July 31, 2023 — An earlier version of this story misstated where J. Robert Oppenheimer was tried before his top-level security clearance was revoked. He appeared before the Atomic Energy Commission, not Congress. It also misstated who contacted the FBI about Oppenheimer. It was William Borden, not Lewis Strauss. Additional context about the investigation and its origins was added.

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