Adolf Hitler's doctor thought he noticed growing signs of insanity in the Nazi leader before the start of World War II and predicted he could become the "the craziest criminal the world ever saw," says a CIA document released Friday.

Later in 1937, the doctor said "the swing towards insanity" seemed to have taken place, according to the memo. The document was among 10,000 pages of information the CIA had gathered on 20 Nazi-era figures. The 10,000 pages of documents in the so-called "personality files" shed light on the extent to which US intelligence services after World War II relied directly or indirectly on suspected Nazi war criminals for information primarily in their drive to garner information on the new enemy, the Soviets.