The hearsay exceptions created by Federal Rule of Evidence 804 or a comparable State rule apply only if the declarant (the maker of the statement) is unavailable to testify at the trial or proceedings at which the declarant's statement is offered.

Cf. Bemis v. Edwards, 45 F.3d 1369, 1373-1374 (9th Cir. 1995) (holding, in plaintiff's civil rights action against defendants city and police officers for use of excessive force, that the trial court properly refused to....If a statement is to fall within the hearsay exception for present sense impressions created by Federal Rule of Evidence 803(1) or a comparable State rule, the maker of the statement -- the declarant -- must personally perceive the event or condition that he or she describes or explains with the statement.

Fed. R. Evid. 609(a)(1) ("(a) General rule. For the purpose of attacking the character for truthfulness of a witness, (1) evidence that a witness other than an accused has been....If a conviction is offered to impeach a witness and the conviction is not for a crime that involves dishonesty or false statement, the conviction of the witness may be used to impeach the witness if the crime for which the witness was convicted is punishable by death or imprisonment for more than a year, if the crime the witness committed is probative of the truthfulness of the witness, and if the opponent fails to show that the risk of prejudice or other harm mentioned in Federal Rule of Evidence 403 outweighs the probative value of the conviction; but if the witness to be impeached is a criminal defendant, the prosecution bears the burden of showing that the probative value of the conviction outweighs the risk of prejudice to the defendant.

Fed. R. Evid. 608.Under some circumstances untruthfulness is admissible to impeach a witness.