In what circumstances will a prosecutor be found to have impermissibly vouched for one or more witnesses?

Second, appellant argues that the prosecutor impermissibly vouched for the credibility of one or more witnesses. Appellant bases this claim on the following principle: "A prosecutor may comment upon the credibility of witnesses based on facts contained in the record, and any reasonable inferences that can be drawn from them, but may not vouch for the credibility of a witness based on personal belief or by referring to evidence outside the record. [Citations.]" (People v. Martinez (2010) 47 Cal.4th 911, 958.) Based on our review of the record, we conclude that the prosecutor presented argument concerning the credibility of witnesses, but in doing so, did not impermissibly vouch for their credibility.