Expert Witnesses (Rule 702)
Rulings about when expert witnesses may testify, the judge's gatekeeping role under Rule 702 (Frye and Daubert), experience-based experts such as police-practices experts, and the limits on experts giving legal conclusions or telling jurors who is telling the truth. Summaries from Criminal Defense Resources™ are general education for pro per/pro se defendants and families, not legal advice.
14 rulings, newest first.
State v. Schoenhardt
In an aggravated assault case where the defendant claimed self-defense, the Arizona Court of Appeals upheld the trial judge's decision to keep out the defense's use-of-force expert, a former police officer with 20 years of experience. The court said the expert's opinions that the defendant's display of a gun was justified and that the other man was the real aggressor were not relevant, because neither person was a police officer, and because experts may not tell jurors how to decide the case. The expert's criticism of the police investigation (not interviewing one witness and not separating witnesses) was properly excluded as a waste of time because it repeated points the jury already heard: the officer testified that separating witnesses and talking to all of them is good police practice, admitted he did not interview that witness, and defense counsel criticized him for not following those practices. Because the issue was raised for the first time on appeal, the court reviewed only for fundamental error.
United States v. Valencia-Lopez
The Ninth Circuit vacated a defendant's four drug convictions and ordered a new trial because the district court let a government expert, an ICE supervisory special agent, testify without making any finding that his key opinion was reliable. The defendant said armed men forced him to drive drugs across the border; the agent testified the chance that traffickers would trust drugs to a coerced driver was "almost nil." The court said the agent's experience was enough to qualify him as an expert, but the record did not show why that experience made this particular opinion reliable, and brushing off objections as "going to the weight" is not a reliability ruling. One judge dissented.
Krause v. County of Mohave
In a civil lawsuit over a deputy's fatal shooting, a federal trial court in Arizona limited the plaintiff's police-practices expert. He could not offer legal conclusions, such as that the force was "not objectively reasonable" or that elements of a legal claim were met. He could not give ballistics or bullet-trajectory opinions, because his police, firearms, and gunsmith experience did not qualify him in that technical field, and he could not testify about medical matters. A new opinion he first gave at his deposition, months after the disclosure deadline, was excluded as untimely. The court found him qualified as a police-practices and use-of-force expert and allowed his testimony on whether deputies violated sheriff's office policies and accepted police practices, short of legal conclusions.
Rascon v. Brookins
In a civil lawsuit against Phoenix police officers over a man's death, a federal trial court in Arizona limited the plaintiffs' police expert, Roger Clark, to law enforcement use of force, training, procedures, and administration. He could not give medical opinions, including on cause of death or the physiological effects of a TASER, which the plaintiffs conceded he was not qualified to give. He could testify about whether the force, including the TASER, was justified and that officers should have acted differently, but could not say the officers acted unconstitutionally or used excessive force, because those are legal conclusions. The same order limited or excluded several other experts.
State v. Bernstein (Herman)
In a special action brought by the State in eleven aggravated DUI cases (the real parties were Doreen Lynn Herman and ten other defendants), the Arizona Supreme Court held that under Arizona Rule of Evidence 702(d), the trial judge, as gatekeeper, must consider whether an expert correctly applied a reliable method to the facts of the case. But mistakes in applying a method justify excluding the evidence only if they make the results themselves unreliable; otherwise the jury weighs them. The trial judge had excluded blood-alcohol results because the lab's gas chromatograph sometimes failed to produce results and had other problems. The Supreme Court said that applied the wrong standard, because the record did not show the defendants' own results were unreliable, and vacated the exclusion order.
State v. Sosnowicz
In a second-degree murder case where the defense was that running over the victim with a vehicle was an accident, the Arizona Court of Appeals held that the medical examiner should not have been allowed to testify that the manner of death was "homicide." He admitted the classification rested on what police told him, not on specialized medical knowledge, so he was in no better position than the jury to decide accident versus homicide, and jurors could take his opinion to mean the defendant was guilty. The court said a manner-of-death opinion based mainly on the autopsy will often be admissible, while one based largely on witness accounts the jury can judge for itself normally will not be. Because the other evidence was very strong, the error was harmless and the convictions were affirmed.
Smith v. City of Hemet
In a civil excessive-force lawsuit, the full Ninth Circuit held that the plaintiff's earlier conviction for resisting or obstructing an officer did not automatically bar his lawsuit, because the force may have been used after the conduct behind the conviction. It also defined "deadly force" as force that creates a substantial risk of causing death or serious bodily injury, and reversed summary judgment for the officers. In deciding the force issue could not be resolved without a trial, the court noted that the plaintiff offered an expert declaration, based on California's Peace Officer Standards and Training, that officers could have used control holds instead of a police dog, and said a rational jury could rely on such evidence. It cited Larez v. City of Los Angeles, 946 F.2d 630 (9th Cir. 1991), and Davis v. Mason County, 927 F.2d 1473 (9th Cir. 1991), for police-practices expert testimony.
Hangarter v. Provident Life & Accident Insurance Co.
In a civil insurance bad-faith case, the Ninth Circuit upheld admission of an insurance-industry expert who testified that the insurer departed from industry standards. The court explained that an expert cannot give a legal conclusion (an opinion on an ultimate issue of law), but this expert never said the insurer acted in bad faith; he testified about industry standards, which supported that finding without stating it. The court also held that for non-scientific testimony like this, Daubert factors such as peer review and error rates may not apply, because reliability depends on the expert's knowledge and experience. The trial judge wrongly said Daubert did not apply at all, but that was harmless because the judge had probed the expert's experience.
United States v. Hankey
In a drug case, the Ninth Circuit upheld letting a police gang expert testify, to show possible bias in a co-defendant's testimony, that members of affiliated gangs who testify against each other are beaten or killed. The court said the Daubert factors (testing, peer review, error rates) did not fit this kind of testimony, whose reliability depends on the expert's knowledge and experience, and that trial judges have broad discretion in how they test reliability. The trial judge had held a hearing, questioned the officer about the basis for his opinions, refused to let him testify about one witness's gang membership for lack of foundation, and gave the jury a limiting instruction.
Kumho Tire Co. v. Carmichael
In a civil tire-failure case, the U.S. Supreme Court held that the trial judge's Daubert gatekeeping duty applies to all expert testimony, including testimony based on technical or other specialized knowledge and on experience, not just scientific testimony. The judge may use the Daubert factors when they help measure reliability, but they are not a required checklist, and the judge has broad latitude in deciding how to test reliability. The Court upheld the exclusion of a tire expert whose method, as applied to this tire, was not shown to be reliable.
State v. Salazar
The Arizona Court of Appeals upheld the exclusion of a defense expert who would have testified that there was a "90 percent" likelihood that a person inexperienced with firearms would be disarmed by an attacker if he tried to use the gun in self-defense. The court saw no connection between that opinion and the defendant's actions or his claimed belief that deadly force was necessary, since there was no evidence he fired because he feared being disarmed. It also said that whether self-defense was reasonable is generally a question for jurors' common sense, so expert testimony on that issue is generally not allowed. The conviction was still reversed for other reasons: the trial judge should have been disqualified, and the defense was wrongly barred from asking two State witnesses about their juvenile probation status to show possible bias.
Daubert v. Merrell Dow Pharmaceuticals, Inc.
In a civil case claiming a prescription drug caused birth defects, the U.S. Supreme Court held that the Federal Rules of Evidence, not Frye's "general acceptance" test, govern expert scientific testimony in federal trials. The trial judge must act as a gatekeeper and make sure the testimony rests on a reliable foundation and fits the issues in the case. Factors the judge may consider include whether the theory or technique can be and has been tested, peer review and publication, the known or potential error rate and standards controlling the technique, and general acceptance. The inquiry is flexible and focuses on methods, not conclusions.
State v. Lindsey
The Arizona Supreme Court held that an expert may explain general behavior patterns of child sexual-abuse victims to help jurors weigh testimony, but may not give an opinion on whether a particular witness is truthful, on the truthfulness of witnesses of that type, or on the percentage of such witnesses who tell the truth. Here the State's expert said most people in her field believe very few incest victims lie and that the likelihood was "very strong" in this case. The court said "the law does not permit expert testimony on how the jury should decide the case," reversed the two incest convictions, and ordered a new trial on those counts. The other convictions were affirmed, but a later supplemental opinion sent them back for resentencing.
Frye v. United States
The court affirmed a second-degree murder conviction and upheld the exclusion of a defense expert who would have testified about the results of a "systolic blood pressure deception test" (an early forerunner of the polygraph) given to the defendant. The court said that expert testimony based on a scientific principle is admissible only if the principle is "sufficiently established to have gained general acceptance in the particular field in which it belongs," and this test had not.
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