Substitute Experts After Smith v. Arizona
How courts apply Smith v. Arizona’s holding that a substitute expert who conveys an absent analyst’s statements in support of an opinion introduces those statements for their truth — the Crawford and Bullcoming line barring surrogate testimony on testimonial forensic certifications — the primary-purpose question Smith remanded over when lab reports and analyst notes are testimonial — the Massachusetts rule that an opinion dependent on a non-testifying analyst’s testimonial hearsay is barred even if the expert reviewed protocols and the case file — the survival of independent opinions built on raw machine-generated data that is not hearsay at all — and Rule 703’s basis-evidence pathway, which cannot define the constitutional inquiry.
Substitute Forensic Expert Testimony After Smith v. Arizona: When Basis Testimony Violates the Confrontation Clause
The Supreme Court held that "[w]hen an expert conveys an absent analyst’s statements in support of his opinion, and the statements provide that support only if true, then the statements come into evidence for their truth" Smith v. Arizona, 602 U.S. 779 (2024). A state evidence rule labeling such basis testimony non-hearsay does not settle the constitutional question: "[e]videntiary rules, though, do not control the inquiry into whether a statement is admitted for its truth," because "[w]here testimonial statements are involved," "the Framers [did not mean] to leave the Sixth Amendment’s protection to the vagaries of the rules of evidence"; a reviewing court must instead "conduct an independent analysis of whether an out-of-court statement was admitted for its truth." The federal analogue of the rejected rationale is Fed. R. Evid. 703, under which an expert "may base an opinion on facts or data in the case that the expert has been made aware of or personally observed"; if experts in the field would reasonably rely on those kinds of facts or data, "they need not be admissible for the opinion to be admitted," and when they are inadmissible "the proponent of the opinion may disclose them to the jury only if their probative value in helping the jury evaluate the opinion substantially outweighs their prejudicial effect." After Smith, that evidentiary pathway cannot carry a testimonial statement past the Confrontation Clause.
Smith completes a line of decisions the Court began two decades ago. Under Crawford v. Washington, 541 U.S. 36 (2004), the Clause "applies to ‘witnesses’ against the accused — in other words, those who ‘bear testimony’" — and "[w]here testimonial evidence is at issue, however, the Sixth Amendment demands what the common law required: unavailability and a prior opportunity for cross-examination." Applying that framework to forensic proof, Bullcoming v. New Mexico, 564 U.S. 647 (2011) held that the prosecution may not introduce "a forensic laboratory report containing a testimonial certification — made for the purpose of proving a particular fact — through the in-court testimony of a scientist who did not sign the certification or perform or observe the test reported in the certification," because "surrogate testimony of that order does not meet the constitutional requirement." A document "created solely for an ‘evidentiary purpose,’ . . . made in aid of a police investigation, ranks as testimonial," and, as Smith reiterated, a defendant’s "ability to subpoena" the absent analyst "is no substitute for the right of confrontation" — the Clause "imposes a burden on the prosecution to present its witnesses, not on the defendant to bring those adverse witnesses into court."
Deciding that the analyst’s statements came in for their truth resolved only half of the inquiry; whether those statements are testimonial is a separate question that the Court remanded. The testimonial issue "focuses on the ‘primary purpose’ of the statement, and in particular on how it relates to a future criminal proceeding," and "[a] court must therefore identify the out-of-court statement introduced, and must determine, given all the ‘relevant circumstances,’ the principal reason it was made" Smith v. Arizona, 602 U.S. 779 (2024). State high courts applying that instruction have rejected the substitute-expert workaround on both fronts. In Commonwealth v. Gordon, 266 N.E.3d 369 (Mass. 2025), the Massachusetts Supreme Judicial Court held that "where a substitute expert's opinion is dependent upon the truth of a nontestifying analyst's testimonial hearsay, the confrontation clause bars admission of the opinion even if the substitute expert is familiar with the testing analyst's laboratory protocols and reviewed the analyst's case file." "Such expert opinion testimony, after Smith, is prohibited because the relevant witness against the accused, in a constitutional sense, is the absent analyst." And on the primary-purpose question, the court concluded that analyst notes "documenting findings, observations, and conclusions made by an analyst at the behest of law enforcement, are testimonial," vacating the conviction and remanding for a new trial.
The line at which substitute-expert testimony survives falls at machine-generated data. Gordon itself observed that the gas chromatography-mass spectrometry printout underlying the absent analyst's work "was not testimonial hearsay," because "[c]omputer-generated records are created solely by the mechanical operation of a computer and do not require human participation." The Kentucky Supreme Court drew the same line for cellphone forensics in Baldwin v. Commonwealth, No. 2023-SC-0544 (Ky. Sept. 18, 2025), holding "as a matter of first impression that raw, machine extracted Cellebrite data that is devoid of any human input, conclusions, or assertions does not implicate the Confrontation Clause because it is not testimonial hearsay." The Clause, "although certainly applicable to forensic evidence, applies only to forensic evidence that is testimonial hearsay," so "any Confrontation Clause inquiry raises two questions: does the evidence at issue constitute hearsay and, if so, is that hearsay testimonial?" An expert who reviews raw output and testifies to her own conclusions conveys no absent analyst’s statements at all — there is no human declarant to confront.
Under these decisions, the constitutional analysis of substitute forensic expert testimony proceeds in two steps, and neither can be finessed by an evidentiary label. A substitute expert may not relay an absent analyst’s factual assertions — descriptions of the samples received, the protocols followed, the tests run, the results recorded — as the basis for an ostensibly independent opinion, because those assertions support the opinion only if true and therefore come into evidence for their truth; and where the underlying records were prepared with the primary purpose of serving a future prosecution, the Confrontation Clause requires the testing analyst herself, not a surrogate, unless she is unavailable and the defendant had a prior opportunity for cross-examination. Neither the non-hearsay label a rule of evidence attaches to basis testimony nor the defendant’s power to subpoena the analyst changes the result. What remains open to prosecutors is narrower: an expert who forms her own conclusions from raw, machine-generated output — a chromatograph printout, a Cellebrite extraction — testifies to no one’s hearsay, and records created for purposes other than proving facts at trial, such as accreditation, internal review, or reminders to self, may fall outside the Clause. A trial team facing an unavailable analyst must therefore retest the evidence, present an expert whose opinion rests on non-hearsay data, or establish unavailability plus a prior opportunity for cross-examination.