A newly declassified document shows that J. Edgar Hoover, the longtime director of the Federal Bureau of Investigation, had a plan to suspend habeas corpus and imprison some 12,000 Americans he suspected of disloyalty. Hoover sent his plan to the White House on July 7, 1950, 12 days after the Korean War began. It envisioned putting suspect Americans in military prisons. Hoover wanted President Harry S. Truman to proclaim the mass arrests necessary to protect the country against treason, espionage and sabotage." The F.B.I would "apprehend all individuals potentially dangerous" to national security, Hoover's proposal said. The arrests would be carried out under "a master warrant attached to a list of names" provided by the bureau. The names were part of an index that Hoover had been compiling for years. "The index now contains approximately twelve thousand individuals, of which approximately ninety-seven per cent are citizens of the United States," he wrote. "In order to make effective these apprehensions, the proclamation suspends the Writ of Habeas Corpus," it said. Habeas corpus, the right to seek relief from illegal detention, has been a fundamental principle of law for seven centuries. Hoover's plan called for "the permanent detention" of the roughly 12,000 suspects at military bases as well as in federal prisons. The prisoners eventually would have had a right to a hearing under the Hoover plan. The hearing board would have been a panel made up of one judge and two citizens. But the hearings "will not be bound by the rules of evidence," his letter noted. The only modern precedent for Hoover's plan was the Palmer Raids of 1920, named after the attorney general at the time. The raids, executed in large part by Hoover's intelligence division, swept up thousands of people suspected of being communists and radicals.