Making Experts Matter
Expert testimony presents several distinct evidentiary opportunities. Perhaps most significantly, experts can present a metaphor that may successfully frame a case. Such verbal pictures or images may be both powerful and persuasive. Additionally, experts can testify about professional standards and whether those standards were met or violated. By doing so, they can ground an advocate’s case in the analysis, and inherent credibility, of a recognized profession.
The distinct opportunities presented by experts extend to cross-examination. Using the expert’s own published words in cross-examination not only may undercut the witness’s credibility, but also can support the substantive litigation positions of the interrogator. Turning the adverse expert into one’s own is a frequent trial maneuver and a highly effective one.
When you speak to the prosecutor, you learn that the government has information that various members of the county commission received bribes to award contracts for the construction of the county commission building. Although she has no specific information that Lewis paid any bribes, Wrongway is one of the prime contractors on the project. If Lewis has something to say, now is the time for him to say it.
Among these ways of using expert testimony, framing the evidence in a case through metaphor may be the most powerful and least widely used. Lawyers commonly introduce metaphors on summation. Many a talented criminal defense attorney has won an acquittal by using images impressed on our minds since childhood. But a metaphor expressed by a witness during trial can be more powerful than one introduced in closing by a lawyer. Metaphors, however, are not ready made. A metaphor that does not fit—or, even worse, an analogy that is misplaced—may be disastrous. The advocate must think very carefully about the problems that must be solved and the points that must be made to prevail.
Consider the defense of a French bank against claims by a group of Venezuelan investors that they lost $19 million in allegedly unauthorized international currency trading. The defense of the case posed numerous questions. How could the lawyer and expert explain the intricacies of international currency trading to a jury? What could have led to millions of dollars of losses in dealings with a bank other than fraud or negligence by the bank? Banks are supposed to be anchors of stability.
In working with the expert to defend the bank, the first relevant metaphor developed was this: Buying international currency is like buying stock. The expert then used that stock metaphor to explain how someone could win or lose money in foreign exchange trading. Along the way, the expert moved from characterizing the Venezuelan investors as investors in stock to gamblers at a casino. The expert was then asked to apply the gambling metaphor to the facts of the case, to explain the plaintiffs’ losses. Through metaphors, the expert depicted the plaintiffs as persons who “made the wrong bet.” This gambling metaphor made a complex and arcane series of losses comprehensible in a manner severely damaging to the plaintiffs.
A lawyer also may use metaphors effectively on cross-examination. This use should be limited, though, to cases in which the lawyer has decided for tactical reasons not to call his or her own expert. Otherwise, it is better to elicit the metaphor on direct examination through the expert who is both friendly and prepared.
Another opportunity at trial provided by experts but not by fact witnesses is the identification of standards that put the expert’s profession squarely behind his or her testimony. The O. J. Simpson trial is instructive in the creative use of standards to support expert testimony at trial. The most formidable challenge facing the Simpson defense lawyers was the trail of blood evidence implicating the renowned football star in the murders. Yet, Simpson’s trial lawyers won his acquittal. Expert testimony and the use of standards allegedly breached are key parts of that success story. The defense sought to take the very strength of DNA analysis, its extraordinary capacity to detect small quantities of DNA, and use it to impeach the technology. The defense never claimed that any of the DNA determined to be Simpson’s was not his. Instead, they argued that it was introduced through planting of blood drops taken from his arm or through contamination made possible by lab personnel’s incomplete understanding of the risks of such contamination.
To show the jury that the DNA at the laboratory of the Los Angeles Police Department (LAPD) could not be trusted, and that the LAPD might have contaminated the evidence, the defense called as an expert Dr. John Gerdes, a Denver biologist who ran a tissue-typing lab. Gerdes occupied an unusual niche among scientists who testify regularly in DNA cases—he believed that certain DNA tests are so sensitive and vulnerable to contamination that they should not be allowed in court, either to clear defendants or to implicate them.
To support the argument that contamination might have taken place despite clean controls, Gerdes offered studies showing contamination in the LAPD crime lab in other cases, and he relied in part on a 1992 report of the National Academy of Sciences on DNA testing. The report also was used to damage the prosecution’s case in one other significant respect. The report had recommended the implementation in the long term of a regulatory program for DNA laboratories, including a procedure in which the labs regularly would be subjected to testing on mock cases that laboratory personnel believed to be genuine. Such testing is known as external blind proficiency testing because it is administered by an outside (thus, “external”) testing agency that measures a laboratory’s proficiency without the lab’s knowledge (that is, on a “blind” basis). The report’s recommendation subsequently had been called into question by the entity that was supposed to implement it, but as of the time of the Simpson trial, no final decision had been made.
The argument that there might have been multiple errors, of course, was something of a stretch. The sheer number of DNA results that typed to Simpson was a compelling argument against laboratory error. Still, the defense had managed to wrap itself into what were purportedly best professional standards while asserting what otherwise would have been a highly implausible defense.
Testimony regarding professional standards is a form of fact testimony. Expert testimony, however, is particularly distinguished from that of fact witnesses because experts can offer opinions. The identification and development of those opinions—although they need not be labeled as such—is fundamental to preparing an expert adequately.
Early on in witness preparation, the lawyer should identify the key take-away points that the jury ideally should remember from the expert’s testimony. Although some must be presented specifically as opinions, the advocate who presents some of those conclusions as facts may be more effective than one who offers them all as the expert’s opinions.
Expert witnesses present particular opportunities not available with fact witnesses, most especially the ability to ask hypothetical questions, which combine with the expert’s opinion testimony to produce compelling evidence. Hypothetical questions highlight for the jury the facts upon which experts base their opinions. The facts selected to underlie the expert’s hypothetical should be facts that the lawyer reasonably believes can and will be proved.
Experts, unlike fact witnesses, frequently provide a rich paper trail for cross-examination. That trail may include several potential paths—publications, prior testimony, and learned treatises, among others. The expert likely will have written books or articles relating to the subject of the expert testimony well before the case was even a glimmer in anyone’s eye. Publications are also fair game for cross even if written by a person other than the testifying expert. The witness may be confronted with learned treatises authored by others, asked if they are authoritative, and potentially impeached with passages from those writings, depending on the governing rules in the jurisdiction.
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Harlan A. Levy is a partner in the New York City office of Boies, Schiller & Flexner LLP. He may be reached at firstname.lastname@example.org.