Theremin saw little of the $100,000 he was paid, Glinsky says, which most likely went straight into Soviet coffers. But he stayed in the US for a while working on other projects, and engaging in industrial espionage.
“His very reason for being sent over was his espionage mission,” says Glinsky. Demonstrating the theremin instrument was just a distraction, a Trojan Horse, as it were.
“He had special access to firms like RCA, GE, Westinghouse, aviation companies and so on, and shared his latest technical know how with representatives from these companies to get them to open up to him about their latest discoveries. […]
Later that year he returned suddenly to the Soviet Union, leaving his wife behind. Some people suggested he’d been kidnapped by Soviet officials, but Glinsky says a combination of debt and homesickness led to Theremin returning voluntarily.
He returned to a Soviet Union in the grip of Stalin’s purges. He was arrested and falsely accused of being a counter-revolutionary, for which he received an eight year sentence in 1939.