The JCP was founded as an underground political association. Outlawed in 1925 with the passage of the Peace Preservation Law, the JCP was subjected to repression and persecution by the Special Higher Police ("Tokkō"), nicknamed the "Thought Police." JCP members and sympathizers were imprisoned and pressured to "convert" ("tenkō suru") to anti-communist nationalism. Many of those who refused to convert remained imprisoned for the duration of the Pacific War. The Japanese Communist Party member Hotsumi Ozaki, who was part of the Richard Sorge spy ring for the Kremlin, was the only Japanese person hanged for treason under the Peace Preservation Law.