"In 1866, the Supreme Court ruled in Ex parte Garland that the pardon power "extends to every offence known to the law, and may be exercised at any time after its commission, either before legal proceedings are taken, or during their pendency, or after conviction and judgment."

Can President Bush pardon people who haven't even been charged with a crime?

Just one of the many links that can be obtained by the use of Google if one is not too lazy.