A person's handwriting may be authenticated by a lay witness -- i.e., a lay witness may identify the author of handwriting -- if the witness is personally familiar with the putative author's handwriting and the witness did not acquire such familiarity for purposes of the litigation.

Fed. R. Evid. 804(b)(1) advisory committee's note ("As a further assurance of fairness in thrusting upon a party the prior handling of the witness, the common law also insisted upon identity of parties, deviating only to the extent of allowing substitution of successors in a narrowly construed privity. Mutuality as an aspect of identity is...In a civil action the hearsay exception for prior testimony can apply even if the prior testimony was offered against another party in the previous proceeding. It is enough if the party against whom the prior testimony was a predecessor in interest that had an opportunity and similar motive to develop the declarant's testimony the in the prior proceeding by direct, cross, or redirect examination.

United States v. Nettles, 476 F.3d 508, 517 (7th Cir. 2007) (convictions for attempting to destroy a building by fire and explosive, and of manufacturing and transferring counterfeit currency; defendant asserted that district court's admission of Ali's statements violated his Confrontation Clause right;...The Sixth Amendment Confrontation Clause places no limits on the admission at trial of nonhearsay statements made prior to or outside of trial.

United States v. Zedner, 401 F.3d 36, 49-50 (2d Cir. 2005) (upholding trial court's admission into evidence of rebuttal witnneses' testimony about accused's previous commission of fraud, where accused claimed lack of criminal intent, and evidence of fraud was relevant to prove accused's "financial...Evidence of a criminal or wrongful act apart from the act that at issue at trial Is not barred by the prohibition against circumstantial use of character if intent, knowledge, mistake, or accident is a legally-material factual issue, the opposing party suggests the non-existence of knowledge or urges mistake or accident as a defense, and evidence of another crime, wrong, or act is offered to prove the knowledge or the absence of mistake or accident by a criminal defendant or other person.