In 1939, the Bureau began compiling a custodial detention list with the names of those who would be taken into custody in the event of war with Axis nations. The majority of the names on the list belonged to Issei community leaders, as the FBI investigation built on an existing Naval Intelligence index that had focused on Japanese Americans in Hawaii and the West Coast, but many German and Italian nationals also found their way onto the secret list. Robert Shivers, head of the Honolulu office, obtained permission from Hoover to start detaining those on the list on December 7, 1941, while bombs were still falling over Pearl Harbor. Mass arrests and searches of homes (in most cases conducted without warrants) began a few hours after the attack, and over the next several weeks more than 5,500 Issei men were taken into FBI custody. On February 19, 1942, President Franklin Roosevelt issued Executive Order 9066, authorizing the removal of Japanese Americans from the West Coast. FBI Director Hoover opposed the subsequent mass removal and confinement of Japanese Americans authorized under Executive Order 9066, but Roosevelt prevailed. The vast majority went along with the subsequent exclusion orders, but in a handful of cases where Japanese Americans refused to obey the new military regulations, FBI agents handled their arrests. The Bureau continued surveillance on Japanese Americans throughout the war, conducting background checks on applicants for resettlement outside camp, and entering the camps (usually without the permission of War Relocation Authority officials) and grooming informants in order to monitor dissidents and "troublemakers." After the war, the FBI was assigned to protect returning Japanese Americans from attacks by hostile white communities.

When did the Bureau begin compiling a custodial detention list?