Not initially. Initially, the prosecutor bringing charges against the defendant has the burden of proving the defendant’s guilt beyond a reasonable doubt. There are instances when the burden of proof can shift to the defendant. For example, the defendant may have committed the alleged crime, but may present an affirmative defense (I.e., self defense, insanity, necessity). At this point, the defendant has the burden of proving the affirmative defense by a preponderance of the evidence (the fact in question is more likely than not to be true), clear and convincing evidence or another evidentiary standard depending on the jurisdiction and the affirmative defense.
