From:

Bear in mind who was making the arrests: the FBI
under J. Edgar "like my dress?" Hoover.

To be fair to J. Edgar, he insisted that the majority of Issei, Nisei and Kibei
would prove to be loyal in the fight with Japan. If there were spies and
sabateurs among them, the FBI could ferret them out through normal
investigations.
The biggest advocates of the mass round-up of Japanese was Earl Warren, then
California state attorney general who went around making inflamatory speeches
charging that the Japanese residents of California were a nest of saboteurs
and traitors. He used the hysteria he whipped up to ride into the governorship
in the 1942 election.


Chris Mark