The phrase “Beyond a reasonable doubt” refers to the standard of proof commonly observed and required in courts of law for the prosecution to establish that the defendant committed the offense claimed. If any reasonable doubt, or the similarly defined, more strictly demanding “shadow of a doubt,” is present in the case, then the prosecution’s case can be defeated.
A basic principle of the U.S. criminal law system is that prosecutors face the burden of proof in arguing their cases, which is established in part by the “beyond a reasonable doubt” principle. As such, the requirement for guilt to be proved beyond a reasonable doubt also acts to protect American civil liberties. In that both the administering judge and the prosecutor will be government employees, “reasonable doubt” requirements are for judicial fairness.