Have you heard of the American Freedom of Information Act? The press here would get hold of your Purple Secret, and they'd publish it. Even if they heard a rumor about it they'd investigate. Nothing could block publication. If someone tried to kill the reporter, they'd publicize that, too. They'd get everybody worked up about it calling their congressmen and senators. Soon the President would have to publish an official report about it. In other words, you couldn't keep the secret.
The Black Vault is a massive research center archiving what the U.S. government is trying to hide... from YOU. One of the biggest sections on The Black Vault is the Freedom of Information Act (FOIA) Government Document archive, spanning more than 650,000 pages of material. You can also view other case files such as: UFOs, Paranormal and Military Activity etc.