Also known as: expert trial witness · expert witnesses · expert witness
Written by attorneys · grounded in primary & secondary sources — see below
A witness who provides opinion testimony based on specialized knowledge, skill, experience, training, or education to help the trier of fact understand evidence or determine a fact in issue.
Esme Ellington faces federal fraud charges. The prosecution calls a forensic accountant to describe transaction patterns and timing. The expert stops short of stating whether Ellington possessed the required intent to defraud. The court admits the testimony because the expert avoided any direct opinion on the mens rea element reserved for the jury.
Eugene Ellsworth stands trial for sexual assault. A state lab analyst testifies that a crime-scene profile matches the defendant's known sample. The analyst relies on a non-testifying lab's raw data only to explain the foundation of her independent conclusion. The court allows the testimony after finding the data served as the basis for the opinion rather than as substantive proof.
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Emmett Egan and Emma Erickson litigate a complex patent infringement suit involving semiconductor design. The court issues an order to show cause why it should not appoint an independent electrical engineer. After both parties submit nominations and the chosen expert consents, the court appoints the specialist to advise on industry standards and file findings with the clerk.
Emanuel Escobar sues Enigma Technologies for product liability after a software failure. The defense expert cites a peer-reviewed engineering journal during direct examination. On cross-examination, plaintiff's counsel confronts the expert with a contrary statement from the same journal. The court permits the statement to be read into evidence once the publication is established as reliable authority.
Emily Ellis faces criminal charges and seeks to introduce polygraph results. The defense offers an expert to explain the systolic blood pressure deception test. The court excludes the testimony after finding the underlying technique lacks general acceptance in the relevant scientific community.
Echelon Security is sued for bad-faith denial of an insurance claim. The plaintiff calls an actuary to quantify the insurer's financial exposure and industry practices. The expert's testimony supports the jury's consideration of reprehensibility and ratio factors when awarding punitive damages.
A party must disclose the identity of any witness it may use at trial to present opinion testimony based on specialized knowledge. The disclosure is required by court order or the default deadlines even if the witness is an employee rather than a retained outsider. Failure to disclose typically results in exclusion unless the omission was substantially justified or harmless.
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For experts who need not submit a full written report, the party must still disclose the subject matter of the expected expert testimony and a summary of the facts and opinions the witness will offer. A bare statement of diagnosis or treatment is insufficient when the witness will give specialized causation or prognosis opinions.
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No. In a criminal case an expert must not state an opinion on whether the defendant possessed a mental state or condition that constitutes an element of the crime or a defense. Those determinations remain exclusively for the trier of fact.
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On a party's motion or on its own initiative the court may order the parties to show cause why an expert should not be appointed and may request nominations. The court may appoint any expert on whom the parties agree or any expert of its own choosing, provided the expert consents to serve.
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…Center conceded liability for the lost transparencies and the issue of damages was tried before a jury. At trial, Gasperini's expert witness testified that the "industry standard" within the photographic publishing community valued a lost transparency at $1,500. See id. , at 227. This industry standard, the expert explained,…