[Jewbacca]

Plenty has been released. There was an active network:

http://www.nytimes.com/1983/05/22/us/1941-cables-boasted-of-japanese-american-spying.html

[Rockingham]

Marching Orders: The Untold Story of World War II, by Bruce Lee, is an accounting of the high level intelligence advisories generated by the American cryptanalysis effort in WW II. No one who was in the know had any doubt that internment of Japanese Americans was justified.