In Branigan’s notes, Joe explained that the reason he needed to see Nelson on such short notice was because those working on the project would soon be relocated to a remote site, and he had been recently selected as one of those to go. The two discussed “the professor,” who Nelson complained was “very much worried now and we make him feel uncomfortable.”
“You won’t hardly believe the change that has taken place,” Joe agreed.
“To my sorrow, his wife is influencing him in the wrong direction,” Steve said.
The discussion then shifted back to “the project.” “Do you happen to know about what kind of materials they are working on?” Steve asked his guest. Joe hesitated before replying that most of the things he knew were already a matter of common knowledge among physicists around the world. Much of that early work had already been published, he said.
Branigan’s notes recorded Nelson’s delicate effort to coax more information from Joe:
STEVE: “Joe, I’d like to ask you, would it be possible for you to give this elementary thing that’s already been published, you know?”
JOE: “Uh, huh.” Long pause.
STEVE: “Could I get a copy of that?”
JOE: “The one that’s published you mean?”
STEVE: “Yeah. Is that possible?
JOE: Long pause. “Now, wait just a second. Pauses. “It’s natural I’m a little bit scared, because…” (trails off)
Joe worried that his Communist background—he had been a member of the party since 1938, he told Steve—would cause him to come under scrutiny by the project’s investigators. Steve said that he had already been told something about the project by the professor: “What the nature of it is—as much as that.” But his informant had been reluctant to discuss the subject, and Nelson had decided not to pressure him.
Finally, Joe gave in. Lowering his voice, he dictated in whispers while Nelson—and Branigan—took notes. The FBI agent strained to hear but was only able to catch and write down snippets: “Separation method is preferably that of the magnetic spectrograph with electrical and magnetic focusing, or less preferably, that of the velocity selector.… sphere 5 centimeters in diameter with material … deuterium.… this design is tentative and is being experimented upon.”91
Joe also told Steve that there was already a separation plant under construction in Tennessee that was expected to employ from 2,000 to 3,000 workers.
Before he left, Joe and Steve discussed the logistics of future meetings. He had a sister in New York, Joe said, and her travels could be used as a cover for subsequent contacts, where he could pass additional information to Steve. Nelson advised Joe that comrades sent to Tennessee and other remote locations should work in teams of two and burn their party books as a precaution. As with Communists serving overseas in the army or navy, the names of those involved in the project would be kept in a secret list, which Steve said he would memorize and then destroy. In parting, Nelson again cautioned Joe not to put anything in writing.92 Cassidy arrived outside Nelson’s house in time only to catch a glimpse of Joe walking out the door.
* * *
Within hours of the meeting between Nelson and Joe, King had couriered a transcript of the conversation to G-2 at the Presidio, where the news hit Pash like a thunderclap. Flying to Washington the following day to personally brief Groves and Lansdale on the incident, Pash believed that the FBI bug provided proof of Oppenheimer’s involvement in an espionage plot.93
Pash assigned Lyall Johnson the task of discovering the identity of Joe. The conversation with Nelson had yielded several valuable clues: Joe had moved to California in 1939, and his wife was from Wisconsin; he had two sisters living in New York City, one of them a teacher.
At the San Francisco FBI office, King asked Branigan and Cassidy to begin immediate round-the-clock physical surveillance of Nelson.94 Aware that the FBI director had been trying since the 1930s to outlaw the Communist Party in the United States as a haven for spies, Pieper wrote Hoover: “I believe a definite possibility exists of developing an espionage case against the CP, USA and the Bureau’s advice is requested.”95
The stakeout of Nelson’s house on Grove Street yielded results the very next morning, April 1, when Nelson walked to a corner drugstore and telephoned the Soviets’ San Francisco consulate from a pay phone. Nelson was overheard using the name “Hugo” and asking to speak with Ivanov; the two agreed to meet at “the usual place” a few days hence.
On the evening of April 6, Branigan and Cassidy followed Nelson to the grounds of St. Joseph Hospital in San Francisco, where Nelson met Ivanov in an open area surrounded by trees.96
Four days later, Cassidy captured another visitor to Nelson’s house on film—a burly figure in an ill-fitting suit whom the FBI later identified as Vassili Zubilin, the recently appointed third secretary of the Soviet embassy in Washington. Despite his lowly title, the bureau suspected Zubilin—who in the United States went by the name “Mr. Cooper”—of being the new NKVD rezident at the embassy.97
The bug in Nelson’s house picked up the Russian counting out bills or bundles of currency, and Branigan recorded this exchange:
NELSON: “Jesus, you count money like a banker.”
UNKNOWN MAN: “Well, after all, I told (deleted), I used to pay out at Russia.”98
For more than an hour, Nelson and Zubilin talked about the Soviet espionage apparatus in America. Nelson said that he had been recruited at the end of 1942 by “a man from Moscow” and that Earl Browder, the head of the Communist Party in the United States, was aware of and supported his mission. He was miffed, Nelson said, that Soviet officials had begun short-circuiting the established apparatus by recruiting rank-and-file members of the party to spy, and instructing them not to inform party superiors of their assignments. Nelson suggested that
