In what circumstances will the court allow a letter to be admitted as evidence?

The letter was not admitted for its truth but only as it bore on the witness's claim of a threat, and the court so instructed the jury. Because the witness claimed the letter contained a threat, whether it actually did so was relevant to his credibility. (See People v. Burgener (2003) 29 Cal.4th 833, 869, 129 Cal.Rptr.2d 747, 62 P.3d 1.) "Inasmuch as the jury was promptly and correctly instructed as to the limited purpose of the evidence, we cannot say that the trial court abused its discretion under Evidence Code section 352 in allowing the testimony." (Id . at p. 870, 129 Cal.Rptr.2d 747, 62 P.3d 1.)