Can a prosecutor vouch for the credibility of a witness by referring to evidence that was not in the record?

It is settled that "[a] prosecutor is prohibited from vouching for the credibility of witnesses or otherwise bolstering the veracity of their testimony by referring to evidence outside the record. [Citations.] Nor is a prosecutor permitted to place the prestige of [his or her] office behind a witness by offering the impression that [he or she] has taken steps to assure a witness's truthfulness at trial. [Citation.] However, so long as a prosecutor's assurances regarding the apparent honesty or reliability of prosecution witnesses are based on the 'facts of [the] record and the inferences reasonably drawn therefrom, rather than any purported personal knowledge or belief,' her comments cannot be characterized as improper vouching. [Citations.]" (People v. Frye (1998) 18 Cal.4th 894, 971.)

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