What is the burden of proving an accomplice to a crime?

If there is evidence from which the jury could find that a witness is an accomplice to the crime charged, the court must instruct the jury on accomplice testimony. The defendant bears the burden to prove, by a preponderance of the evidence, that a particular witness was an accomplice whose testimony requires corroboration. (People v. Williams (1997) 16 Cal.4th 153, 247.)

A witness's mere knowledge of a defendant's criminal intent, without more, does not satisfy this burden. Nor is the witness's presence at the scene, or failure to prevent a crime, sufficient to demonstrate guilt as an aider and abettor. (People v. Nguyen (1993) 21 Cal.App.4th 518, 529-530.)