Also known as: expert witness · expert-witness testimony
Written by attorneys · grounded in primary & secondary sources — see below
A witness qualified by knowledge, skill, experience, training, or education who may provide opinion testimony if the specialized knowledge will help the trier of fact understand the evidence or determine a fact in issue, the testimony rests on sufficient facts or data, it is the product of reliable principles and methods, and the expert has reliably applied those principles and methods to the facts of the case.
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Prosecutors charged Ella Emerson with mail fraud after she allegedly diverted restricted donations. The government called an accounting expert who reviewed ledgers and described the timing and pattern of transfers out of restricted accounts. On direct examination the expert stopped short of stating whether Ella had formed the intent to deprive donors of the funds, leaving that inference for the jury alone.
In a murder prosecution, the state lab generated a DNA profile from crime-scene evidence. A testifying expert relied on a separate profile produced by a non-testifying laboratory to form her own opinion that the profiles matched. The court admitted the expert's testimony because the out-of-court report served only as the basis for her independent conclusion and was not offered for its truth.
Northern Fiber faced a class action alleging misrepresented network capacity. After the parties' engineers produced conflicting throughput measurements, the court on its own motion ordered the parties to show cause why a neutral specialist should not be appointed. The court selected an agreed-upon network engineer who consented to serve and advised the parties of her findings.
During the trial of a products-liability claim, defense counsel called an aerospace engineer to the stand. On cross-examination plaintiff's counsel directed the expert to a statement in a recognized engineering treatise concerning orbital-stability tolerances. The expert acknowledged the treatise as authoritative, and counsel read the statement into the record.
After a minivan rollover, plaintiffs offered an engineer who attributed the accident to a manufacturing defect in the tire. The court examined whether the expert's methodology was reliable under the same gatekeeping standards that apply to scientific testimony, focusing on whether the principles and methods were tied to the facts of the case rather than to general experience alone.
In a criminal trial the defense sought to introduce polygraph results through an examiner who claimed the technique was generally accepted in the scientific community. The court required the proponent to demonstrate that the underlying principles enjoyed general acceptance among experts in the field before admitting the testimony.
On a party's motion or on its own, the court may order the parties to show cause why expert witnesses should not be appointed and may ask the parties to submit nominations. The court may appoint any expert that the parties agree on and any of its own choosing, provided the expert consents to act.
In a criminal case an expert witness must not state an opinion about whether the defendant did or did not have a mental state or condition that constitutes an element of the crime charged or of a defense. Those matters are for the trier of fact alone.
…"gatekeeping" determination limited to "scientific" knowledge. Daubert pointed out that Federal Rules 702 and 703 grant expert witnesses testimonial latitude unavailable to other witnesses on the "assumption that the expert's opinion will have a reliable basis in the knowledge and experience of his discipline." Id. , at 592…
…district court, applying our opinion in United States v. Downing , 753 F.2d 1224 (3d Cir.1985), limited the testimony of his
…a working enterprise, rather than slowly forcing it into bankruptcy while most of its money is spent on asbestos lawyers and expert witnesses
…to examine him. Smith objected to this imposition of the insanity defense. At trial, when the court-appointed expert witness was called to testify, the court instructed the jury that, when a defendant interposes the defense of insanity, the court must appoint an
…last Term in Delaware v. Fensterer, supra . In that case, the defendant was convicted in part on the testimony of the State's
The disclosure must identify the subject matter on which the witness is expected to present expert evidence and provide a summary of the facts and opinions to which the witness is expected to testify.
When a party withholds an expert from the required disclosures, the usual consequence is exclusion of that expert's testimony unless the failure was substantially justified or harmless.
An expert may rely on the profile when it is used only as the basis for the expert's independent opinion that it matches a profile generated by a state lab and the out-of-court report is not offered for the truth of the matter asserted.