from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
BURDEN OF PROOF. This phrase is employed to signify the duty of proving the
facts in dispute on an issue raised between the parties in a cause.
2. The burden of proof always lies on the party who takes the
affirmative in pleading. 1 Mass. 71, 335; 4 Mass. 593; 9 Pick. 39.
3. In criminal cases, as every man is presumed to be innocent until the
contrary is proved, the burden of proof rests on the prosecutor, unless a
different provision is expressly made by statute. 12 Wheat. See Onus
probandi.