National Security and FBI Surveillance Enemy Aliens
The Custodial Detention Index (CDI), or Custodial Detention List was formed in 1939-1941, in the frame of a program called variously the "Custodial Detention Program" or "Alien Enemy Control." J. Edgar Hoover described it as having come from his resurrected General Intelligence Division—"This division has now compiled extensive indices of individuals, groups, and organizations engaged in subversive activities, in espionage activities, or any activities that are possibly detrimental to the internal security of the United States. The Indexes have been arranged not only alphabetically but also geographically, so that at any rate, should we enter into the conflict abroad, we would be able to go into any of these communities and identify individuals or groups who might be a source of grave danger to the security of this country. These indexes will be extremely important and valuable in a grave emergency."