while at caltech, tsien had secretly attended meetings with j. robert oppenheimer's brother frank oppenheimer, jack parsons, and frank malina that were organized by the russian-born jewish chemist sidney weinbaum and called professional unit 122 of the pasadena communist party. weinbaum's trial commenced on august 30 and both frank oppenheimer and parsons testified against him. weinbaum was convicted of perjury and sentenced to four years. tsien was taken into custody on september 6, 1950 for questioning and for two weeks detained at terminal island, a low-security united states federal prison near the ports of los angeles and long beach.