Federal Rule of Evidence 901(b)(4) and comparable State rules allow a thing or matter to be authenticated by its distinctive characteristics considered in conjunction with circumstances.

Fed. R. Evid. 703 advisory committee's note ("Facts or data upon which expert opinions are based may, under the rule, be derived from three possible sources. ... The third source contemplated by the rule consists of presentation of data to the expert outside of court and other than by his own perception. In this respect the rule is...An expert witness may base his or her opinion on hearsay evidence if the hearsay evidence relied on by the witness is the type of hearsay customarily and reasonably relied on by experts in the witness's field.

United States v. Ochoa, 229 F.3d 631, 637-638 (7th Cir. 2000) (upholding trial court's admission of co-conspirator McLaughlin's out-of-court statements because the co-conspirator was unavailable for purposes of the....For purposes of the hearsay exceptions created by Federal Rule of Evidence 804 or a comparable State rule a declarant is "unavailable" within the meaning of Rule 804(a) or a comparable State rule if the declarant (1) is exempted by ruling of the court on the ground of privilege from testifying concerning the subject matter of the declarant's statement; or (2) persists in refusing to testify concerning the subject matter of the declarant's statement despite an order of the court to do so; or (3) testifies to a lack of memory of the subject matter of the declarant's statement; or (4) is unable to be present or to testify at the hearing because of death or then existing physical or mental illness or infirmity; or (5) is absent from the hearing and the proponent of a statement has been unable to procure the declarant's attendance (or in the case of a hearsay exception under subdivision (b)(2), (3), or (4) of Rule 804(b) or a comparable State rule, the declarant's attendance or testimony) by process or other reasonable means; but a declarant is not "unavailable" if such exemption, refusal, claim of lack of memory, inability, or absence is due to the procurement or wrongdoing of the proponent of a statement for the purpose of preventing the witness from attending or testifying.

Shaw v. Mast Advertising & Publishing, 715 F. Supp. 1503, 1505 (D. Kan. 1989) (holding, in plaintiff employee's retaliation action against defendant employer, that evidence of settlement [of witness's claim] was admissible because it....Although settlement negotiations and offers are inadmissible (i) to show the validity or invalidity of a claim when validity is in dispute, (ii) to show the amount of damages when the amount is in dispute, or (iii) to impeach by showing a prior inconsistent statement or specific contradiction, such settlement offers and negotiations are admissible if they are used to impeach a witness by showing the bias or interest of the witness.