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Expert Witnesses: Who You Gonna Call?

Sahith Mocharla

Edited by Ishika Bhatia and Vedanth Ramabhadran

Who you gonna call? In this case, perhaps, not a ghostbuster, but the United States (and countries around the world) have a long and storied history of calling upon the experts of their chosen field to dictate and determine the outcomes of cases. An expert witness is “a person who is permitted to testify at a trial because of special knowledge or proficiency in a particular field that is relevant to the case” [1]. From forensic anthropologists to bona fide lip readers, experts come from all fields and backgrounds, each one reflecting a passion borne of niche-interest and intense dedication. 

Court cases typically follow an established procedure, wherein the facts of a case are presented to a jury – including evidence & witness testimony(s) – to prove that a defendant has (or hasn’t) committed a crime [2]. Prosecutors and Attorneys will call upon two types of witnesses: Lay witnesses, who are called upon to testify their knowledge of the case at hand – circumstantial evidence, eyewitness testimony, and recounting the specific events and context of the alleged crime – and expert witnesses, who are called upon for their intrinsic knowledge, extensive study, and familiarity with the nuances of the field of concern. Crucially, while lay witnesses are seldom, if ever, called upon to testify using their opinion, expert witnesses are called upon to testify solely for their opinion. Their opinion, while not necessarily taken as fact – the same way data or hard evidence might – can still be stated and often very persuasive in helping convince a jury of the prosecution or defense arguments [3]. Within this procedure, expert witnesses fall broadly under two categories – testifying or non-testifying – the former typically provides their expertise during a trial in front of the judge and jury whereas the latter addresses a specific side, primarily in an advisory capacity, offering support during pre-trial preparations. 

Expert testimony came to the fore in the case of Frye v. United States (1923). Mr. Frye was convicted of murder (second-degree) after his usage of a systolic blood pressure deception test (early form lie detection test) – to prove his innocence – was held as inadmissible by a lower court. The Court eventually reasoned that regardless of scientific basis – which the deception test did have – without an established place in science, tests were still in the amorphous blurred realm between experimental science and demonstrated science, ergo, because the test wasn’t ‘sufficiently established’ any testimony utilizing its findings is inadmissible [4]. In 1923 Frye established the standard for expert testimony and its admissibility in a court of law – essentially any scientific (expert) testimony must have broad recognition and usage before being used and upheld in a court; however, Frye has met with and dealt with significant criticisms, most notably in Daubert v. Merrell Dow Pharmaceuticals. In Daubert two parents and their children alleged that the mother’s prenatal ingestion of bendectin (a drug sold by Merrell Dow Pharmaceuticals) had caused serious birth defects. The Daubert’s cited numerous well-credentialed experts in response to the scientific literature provided by the defendant; however, the Court determined that this evidence didn’t meet the applicable general acceptance standard for expert testimony. After a concurring ruling by the Court of Appeals, a new standard beyond Frye was adopted – the Federal Rules of Evidence (FRE) [5]. The Daubert Standard has usurped the Frye Standard (although Frye is still the prime law in some states); Daubert, adopted by the Supreme Court of the United States, allows for a broader interpretation of factors for the reliability of new technology [6]. The Daubert case formulated a standard beyond Frye’s, a more comprehensive approach wherein judges must scrutinize the methodology and scientific principles. For example, under the Frye Standard, fingerprints couldn’t gain widespread use despite its reliability as evidence, whereas it is permissible under the Daubert Standard far sooner which simply requires relevance and reliability, eschewing ‘widespread adoption.’

Yet expertise itself comes in many forms, from technological geniuses to forensic scientists and even lip readers. O.J. Simpson famously brought Dr. Henry Lee – a forensic scientist – to testify about specific evidence in the case regarding blood spatter and circumstantial DNA. Dr. Lee’s speciality – indeed he had made a career of testifying in various capacities – was blood splatter interpretation. Dr. Lee would analyze the ‘splatter’ of blood in a crime scene and ascertain and assert the nature of injury which would’ve caused specific forensic remains [7]. If this science sounds dubious, you aren’t alone, yet its flimsy legal standing is further exacerbated by ‘ambulance-chasers’ – people who often exploit legal loopholes or procedure for financial gain – in fact, Dr. Lee himself was later found liable of fabricating evidence in a murder case which eventually sent two Connecticut men to prison [8]. Although expert witnesses play a key role in our justice system, offering nuance and testimony in situations where pure fact alone may not be sufficient to determine an outcome – due to an insufficiency or another deficiency – their undefined and nebulous role allows for crafty and unscrupulous individuals to exploit an ever expansive system.

The future role of expert witnesses may prove to be even more critical; with the rise of social media and AI, including the advent of deepfake technology, a whole new litany of experts will be necessary to help ascertain what a jury cannot. From being able to interpret and analyze social media content; ascertain and identify digital evidence or security breaches; and machine learning processes, legitimate generations vs human produced work, and real vs created videos (deep fakes); social media, cybersecurity, and defamation experts may be in more demand than ever. Deep fakes and defamation especially run rampant with a government unable to keep up with a rapidly evolving field of technology and innovation, people who are able to persuade and convince a jury that they are able to ascertain the differences between human and algorithmically produced content will be in immense demand. Whether it's Taylor Swift facing unspeakable depictions of her likeness by AIs or Air Canada facing accountability for the rewards program created by its AI chatbot, our social and legal world will begin to include people who claim to know something you don’t, but rest assured, they’ll help you learn what they know too. 

In the intricate web of legal proceedings, societal conceptualizations, and democratic processes, expert witnesses stand as a barometer of our society – in some cases niche and nuanced expert plying their trade to extract justice where no one else can find it, and in others finding ghosts in empty rooms – they’re the specialized responders when legal matters become otherworldly in complexity, often helping elucidating complex matters and providing crucial insight to aid judges and juries. Our society often relies on witnesses to provide understanding for a case, expert witnesses help demystify complex evidence and contribute to the pursuit of truth. Moreover, expert witnesses serve as a bridge between the specialized knowledge within their domain and the broader understanding required in legal proceedings. By leveraging their expertise, expert witnesses contribute to the effective functioning of democracy, promoting the principles of justice, fairness, and the rule of law. Their role extends beyond individual cases, influencing the development and interpretation of laws, thus shaping the legal landscape of a society. As we navigate the intricate intersection of law, society, and democracy, the importance of expert witnesses remains paramount – they are, indeed, the ones you're gonna call when legal matters take an unbelievable turn.


[1] Expert witness - Quick search results | Oxford English Dictionary, (last visited Feb 26, 2024).

[2] U.S. Attorneys | Trial | United States Department of Justice, (2014), (last visited Feb 26, 2024).

[3] Expert witness, LII / Legal Information Institute, (last visited Feb 26, 2024).

[4] Frye v. United States | Case Brief for Law Students | Casebriefs, (last visited Feb 26, 2024).

[5] Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), Justia Law, (last visited Feb 27, 2024).

[6] Frye Standard, LII / Legal Information Institute, (last visited Feb 27, 2024).

[7] Testimony of Dr. Henry Lee in the O. J. Simpson case., (last visited Feb 27, 2024).

[8] Pat Eaton-Robb, Judge Finds Forensic Scientist Henry Lee Liable for Fabricating Evidence in Murder Case, NBC Connecticut (Jul. 21, 2023), (last visited Feb 27, 2024).

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