A statement of an unavailable declarant is not barred by the hearsay rule if the opposing party deliberately acted to prevent the declarant from testifying.

United States v. Quattrone, 441 F.3d 153, 191 (2d Cir. 2006) (upholding trial court's exclusion of "similar reinforcing emails" evidence because it was "insufficient to establish within the meaning of Federal Rule of Evidence 406 a habit of reflexively responding to subordinates' email suggestions.").If a pattern of behavior of a natural person does not rise to the status of a habit, it may constitute a character trait and such non-habitual behavior may be barred by the prohibition against circumstantial character evidence.

United States v. Feliz, 467 F.3d 227, 236-237 (2d Cir. 2006) (upholding trial court's admission of autopsy reports [which were prepared by medical examiners] as business records because they were "'reports kept in the....There is a hearsay exception for a memorandum, report, record, or data compilation, in any form, of acts, events, conditions, opinions, or diagnoses, made at or near the time by, or from information transmitted by, a person with knowledge, if kept in the course of a regularly conducted activity of a business, institution, association, profession, occupation, or calling if it was the regular practice of that business, institution, association, profession, occupation, or calling to make the memorandum, report, record or data compilation, unless the source of information or the method or circumstances of preparation indicate lack of trustworthiness.

Fed. R. Evid. 405(a) & (b) ("(a) Reputation or opinion. In all cases in which evidence of character or a trait of character of a person is admissible, proof may be made by testimony as to reputation or by testimony in the form of an opinion. On cross-examination, inquiry is allowable into relevant specific instances of conduct. (b)...When an exception to the character evidence prohibition makes evidence of a criminal defedant's character admissible, the testimony of a witness on direct examination about the defendant's character must take the form of reputation or opinion and it cannot consist of specific instances of the defendant's conduct.