The Power of a Defense Expert
By Tess Cohen
A medical examiner declares cause of death. A DNA expert explains the likelihood of a match. A translator explains the meaning of a word in a foreign language. Criminal trials often hinge on the testimony of expert witnesses such as these, and all too often lawyers presume that the testimony of experts is true.
But reliance on flawed expert testimony and junk science has been the source many wrongful convictions and, tragically, executions. The “science” behind shaken baby syndrome, arson forensics, and bite mark analysis, to name a few, has come into question as the criminal justice system reckons with the tragedies that have followed the unquestioned acceptance of an expert as a speaker of truth. Despite increased awarness of these problems, newer and more creative forms of junk science are cropping up, including an appalling trend towards analysis of 911 calls that claims to reveal whether, based on speech patterns, individuals are lying during their call for help.
Juries are deferential to experts, and lawyers for either side often lack the expertise themselves to differentiate truth from fiction. Thus, it is of vital importance that in a case where an expert’s testimony is essential to the prosecution’s case, that the defense team explore hiring their own expert.
As an example of the power defense experts can have, the prosecution team who falsely charged ZMO Law client Tracy McCarter with murder, repeatedly—and incorrectly—insisted that according to the medical examiner how Ms. McCarter explained the death of her abusive, estranged husband occurred was inconsistent with the evidence. We, in turn, hired our own expert—a medical examiner who testified frequently for prosecutors—who provided crucial explanations that ultimately were a key part of the prosecution’s decision to drop the charges against Ms. McCarter.
In fact, our defense expert met with prosecutors to explain his findings, and was not only able to articulate the physical evidence matched Ms. McCarter’s memory of the incident, but also why it was more likely that it occurred as Ms. McCarter stated, rather than as theorized by the prosecution.
The Office of the Chief Medical Examiner for New York City (“OCME”) is entirely separate from the District Attorney’s Office, and the prosecution’s medical examiner—as they typically to do—spoke to our team as we were preparing for trial. But by consulting an expert before our discussion with this key prosecution witness, we were able to ask the right questions (and, as it turns out, learn that properly explained the prosecution’s medical examiner also agreed that Ms. McCarter’s recollection of events was consistent with the evidence).
A defense team ideally will consult an expert even when they have no intention of calling one at trial. An expert can help a defense attorney develop cross examination to display the potential errors in expert testimony.
Defense lawyers at ZMO Law PLLC have seen cases where things as simple as an error of time zones changed the importance of a specific text, a word in a foreign language could be translated in two different ways (one far more harmful to the defense), and a narcotics expert claimed an ambiguous word refers to a specific drug. (The use of senior narcotics law enforcement officers as “narcotics experts” has its own separate issues—worthy of its own blog post). Often a well researched cross examination with the assistance of experts is sufficient to undo the damage the prosecution’s expert testimony can cause, and having a defense expert on standby to testify as needed can be a backup if a prosecution expert doubles down on flawed analysis during testimony.
A defense team must approach the prosecution’s expert testimony with skepticism because an expert who is wrong can have devastating effects.
As always, ZMO Law PLLC is available to those charged with crimes involving expert testimony in New York federal and state courts.