The United States Courts website states that the standard of proof in a criminal case is "beyond a reasonable doubt." This level or proof means that the evidence against the defendant is strong enough that there is no reasonable doubt as to the individual's guilt.
The burden to meet the standard of proof required by U.S. courts lies with the prosecutor handling the case. The prosecutor must present ample evidence to build up to the standard of proof throughout the pre-trial and during the trial. The defendant may attempt to have the evidence removed by suppressing it or challenging it directly.