California Further Defines the Hearsay Rules for an Expert Witness

The hearsay rules can be a constant source of confusion for attorneys across the country. Even more so when an expert witness is involved. At issue is whether case-specific statements made by an expert witness, which form the basis of their expert opinion, qualify as testimonial hearsay and thus violate the Confrontation Clause.


In People v. Sanchez, police arrest Marco Arturo Sanchez and charge him with possession of a firearm by a felon, possession of drugs while armed with a loaded firearm, active participation in the Delhi street gang, and commission of a felony for the benefit of the Delhi gang.[1] During trial, the prosecution brings in Detective David Stow to testify as an expert in gang related activities. Detective Stow’s expertise in gang activity is not questioned, but rather the case-specific facts he cites as a basis for his expert opinion in this case are questioned. Detective Stow testifies that based on five documented police contacts that defendant had between 2007 and 2009, that defendant was involved as a member of the Delhi gang. Detective Stow further testifies that he did not know the defendant and was not present for any of these police contacts.

Issue and Analysis

The central issue surrounding this testimony is whether the expert testimony involving these police documents is being used to assert the truth of the matter asserted within the documents, and if so, does the testimony fall into the category of testimonial hearsay. The basic definition of hearsay is an out-of-court statement offered for the truth of the matter asserted. An expert witness is generally given more latitude when testifying about matters within their personal knowledge. The court finds the problem here to be that Detective Stow is reciting case-specific facts with which he has no personal knowledge. The jury is then being given a limiting instruction that Detective Stow’s testimony covering the contents of the police reports in no way corroborates the proof of the reports. The court points out that this is illogical as on the one hand the prosecution is asking the jury to believe the expert witness, whose testimony is based on the accuracy of those police documents, while on the other hand the judge is giving the jury a limiting instruction telling them that the same documents may not have truthful information. The jury must consider expert testimony for its truth because otherwise they will question the credibility of the expert witness.

The court goes on to establish that if this is the case, then the testimony has to be tested under hearsay rules as the Detective is testifying to case-specific out-of-court statements that form the basis of his expert opinion in this case. Here, the information contained within the police documents qualify as testimonial hearsay, as the police interrogation was formal in nature and prepared with an eye for possible future prosecution. This then causes a Sixth Amendment Confrontation Clause issue since the defendant was not given a chance to cross-examine the officers who had first-hand knowledge of the incidents, nor were the officers specifically unavailable.


Because of these violations of the hearsay rules and the Confrontation Clause, the court held that harmful error had occurred. The court reversed the findings relating to the street gang involvement and remanded to the Court of Appeal for further proceedings.

Rule of Law

The court sets forth a bright line rule with respect to expert witness testimony: “When an expert relates to the jury case-specific out-of-court statements, and treats the content of those statements as true and accurate to support the expert’s opinion, the statements are hearsay. It cannot logically be maintained that the statements are not being admitted for their truth. If the case is one in which a prosecution expert seeks to relate testimonial hearsay, there is a confrontation clause violation unless (1) there is a showing of unavailability and (2) the defendant had a prior opportunity for cross-examination, or forfeited that right by wrongdoing.”


The important takeaway from this case is to be careful with your expert witness. Make sure they are not tying their testimony to case-specific facts. If there is testimonial hearsay involved, make sure to take care of the Confrontation Clause issue and make sure the defendant has a chance to cross-examine the declarant. California did not invent new hearsay rules in this case, they simply refined what was already there to make sure the defendant’s rights were not curtailed.

[1] People v. Sanchez, 374 P.3d 320 (Cal. 2016).

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