“For the privilege to apply, however, the government must try to compel a person to make a ‘testimonial’ statement that would tend to incriminate him or her. When a person has a valid privilege against self-incrimination, nobody — not even a judge — can force the witness to give that information to the government. But a communication is ‘testimonial’ only when it reveals the contents of your mind. We can’t invoke the privilege against self-incrimination to prevent the government from collecting biometrics like fingerprints, DNA samples, or voice exemplars. Why? Because the courts have decided that this evidence doesn’t reveal anything you know. It’s not testimonial.”
