‘Man on Wire’: Navigating the pitfalls of expert testimony

Did you ever see the documentary "Man on Wire"? It follows the remarkable journey of Philippe Petit, a famously brave (mad?) tightrope walker who, in 1974, rigged a high-wire between the newly constructed twin towers of New York City's World Trade Center and walked back and forth, 1,350 feet in the air, for 45 minutes -- without a harness or a net! It's breathtakingly suspenseful, and captures a remarkable feat for which Petit was later arrested by spellbound policemen. Part of the thrill of the story is watching Petit navigate unexpected obstacles that spring up as he prepares for his stunt -- like posing as a journalist and a construction worker to gain access to the uppermost facade of the building; devising a bow and arrow to shoot the wire from one tower to the other; and an unexpected night watchman and an undesirable sag in the wire that threaten to derail the entire mission at the last minute.

Lawyering is hardly this dramatic, but the movie offers an analogy to the tightrope a lawyer must walk when presenting expert testimony -- albeit with vastly disproportionate stakes. While some hazards of offering and defending against expert evidence are well-trod, e.g., expert qualifications, other risks are not so obvious, and California appellate courts continue to redefine the rules shaping what practitioners must be wary of.

Let's start with People v. Sanchez, 63 Cal. 4th 665 (2016), one of the hottest topics in expert evidence these days. Sanchez held to be inadmissible hearsay the testimony of an expert witness on gang affiliations which related the individual defendant's gang contacts from prior arrest reports. Sanchez both reaffirmed what the law had always been and changed the way courts and lawyers talk about it. It confirmed what lawyers and courts should already have known -- that an expert cannot simply be a conduit by which otherwise inadmissible hearsay is admitted. But it clarified this rule and provided a vocabulary by which courts and lawyers can evaluate improper expert hearsay claims -- an expert cannot relay "case-specific" hearsay information about which she has no independent knowledge.

At the same time, Sanchez exhibits a tension with the longstanding rule that experts can rely on hearsay. See People v. Perez, 4 Cal. 5th 421, 456 (2018) (dicta: "an expert may nonetheless 'rely on hearsay in forming an opinion, and may tell the jury in general terms that he did so' without violating hearsay rules," citing Sanchez at 684 (emphasis in original); coroner's colleague who had not participated in the autopsy testified based on the autopsy report; finding evidentiary error, if there was any, to be harmless).

Four years after Sanchez, appellate courts are still struggling to determine how it applies and what its limits are. Two recent cases illustrate one such reverberation, and collectively provide a cautionary tale for practitioners about hidden pitfalls in proffering and defending against expert witness testimony in the post-Sanchez era.

In People v. Anthony, 32 Cal. App. 5th 1102, 1139-40 (Cal. App. 2nd Dist., Div. 2, 2019), a gang expert testified at trial about two gangs' activities and their rivalry, relying largely on hearsay information including potentially "case-specific" police reports. The Court of Appeal held that there was no Sanchez error because the expert was "silent on the source of [his] information." So, from Anthony, we learn that silence about the underlying factual predicate may ensure that an expert's testimony gets and stays admitted.

That's all well and good, but what if the defense attorney in Anthony had objected to the gang expert's testimony on the ground that it lacked foundation and that his opinion had no evidentiary value because it was unaccompanied by a reasoned explanation connecting the factual predicates to the ultimate conclusion? This was the winning argument in Fernandez v. Alexander, 31 Cal. App. 5th 770 (Cal. App. 2nd Dist., Div. 8, 2019). There, plaintiff sued her doctor for medical malpractice in treating her wrist. The doctor moved for summary judgment, providing an expert's declaration that the wrist deformity plaintiff claimed to have sustained as a result of the doctor's alleged negligence was a risk even absent any negligence. Plaintiff responded with an expert declaration opining that "based on the records and [the expert's] training," in his opinion to a reasonable degree of medical probability, defendant "caused Plaintiff's further deformity of her left wrist." The Court of Appeal held that plaintiff's expert's declaration was insufficient to raise a triable issue as to causation. The fatal flaw, in the court's view, was that the expert's testimony was "purely conclusory," containing no "reasoned explanation connecting the factual predicates to the ultimate conclusion."

This issue can be especially significant on appeal. An appellant seeking relief based on an evidentiary error must show objection, error and prejudice -- that is, absent the error, "a different result would have been probable.'" F.P. v. Monier, 3 Cal. 5th 1099, 1107-08 (2017); Cal. Const., article VI, Section 13; CCP Section 475. An error in the admission or exclusion of expert testimony is more likely to be prejudicial than an ordinary evidentiary error. This is rooted in the very nature of expert testimony. Experts inherently carry an accreditation and gravitas in the eyes of the jury and the court -- making their testimony weightier and conveying an imprimatur of the underlying subject matter. See, e.g., U.S. v. Freeman, 498 F.3d 893, 903 (9th Cir. 2007) ("expert testimony is 'likely to carry special weight with the jury'" and "an imprimatur of scientific or technical validity to the entirety of his testimony"). As most practitioners know, for better or worse, expert testimony can be very significant, often outweighing other evidence. If there is an objection and error, a different result is often probable. So an evidentiary error on the admissibility of expert testimony will more often result in a reversal, sending its proponent right back to where they began. That may not be as terrifying as falling to your death off a 1,350-foot high-wire, but it is still pretty distressing if you're on the wrong end of that appellate decision and forced to retry your case or worse.

The lesson? When traveling the metaphorical tightrope of expert testimony, be mindful of pitfalls on both sides -- an expert may avoid a Sanchez error by remaining silent about the hearsay information underlying her opinion. But in doing so, she may inadvertently slight the equally important foundational requirement, running afoul of the lesson of Fernandez: an expert's testimony is only as good as the factual predicate and reasoned explanation upon which it rests. That means that in proffering expert testimony, you must be aware of both the Sanchez and foundation chasms. Of course, if defending against expert testimony, you're equally wise to keep these lessons in mind -- raising objections on both Sanchez/hearsay and foundation grounds -- to optimize your chances of having the testimony excluded.

So be prepared and mind the pitfalls on either side -- hearsay on one and foundation on the other. 