Expert Witness

In the movie My Cousin Vinny, a girl walks into the witness box and proceeds to undo the evidence of an Expert Witness. Because she works in her father’s and brother’s workshop, she can help acquit two men who are wrongly accused of murder (Smith, 2002). When I read for my MSc in Forensic Science one module covered how to testify in court. We held a mock court case, where trainee lawyers interviewed trainee forensic scientists. I would like to say I performed well under pressure, but the trainee lawyers tore my report apart in the courtroom. Even after seeing that movie, I made all the mistakes. If it had been a real case, then someone who was a danger to the community might have been set free. So what does it take to be an Expert Witness?

What is an Expert Witness?

The dictionary definition is clear.  “An Expert Witness is one who is qualified in a particular area of Knowledge.” See Image 1.

Image 1: Definition of an Expert Witness
Credit: (COPFS, 2023)

It refers to qualifications and practice in a certain type of knowledge. But from my experience retold above, it is possible to see that knowledge is not the only thing required. Presentations made to my peers are very different propositions to presenting necessary evidence, accurately in court. If there is the smallest doubt in evidence, then it is the lawyers’ job to find it (COPFS, 2023).

Types of Witness in a Court of Law

Lay Witness or Eye Witness

The testimony of Lay Witnesses in a court of law is about giving evidence on what the witness has seen or experienced. They have no qualifications other than being present at the crime scene.

Image 2: A witness gives testimony in court.
Credit: https://commons.wikimedia.org/wiki/File:Scene_in_a_New_Hampshire_court.-General_Pierce_examining_a_witness._Scene_in_a_New_Hampshire_village.-Pierce_the_good_Samaritan_LCCN2008661553.jpg

However, each person who witnesses an incident brings personal bias to their statement. So while their evidence can be valuable it must also be approached with care (Laney, 2023). It might surprise you that a police officer giving testimony is often considered a Lay Witness (Guthrie, 2007).

Character Witness

Character Witnesses are people who know the defendant, and can speak in court about aspects of the defendant’s personality and reputation. Perhaps they will relate a tale showing how the defendant acted in similar or relevant situations. A character witness can speak for or against the defendant, but they have no direct contact with the alleged crime (LII).

And finally,

Expect Witness

As mentioned above in the definition, an Expert Witness is in court to speak on some aspect of their knowledge and experience that is related to the crime (COPFS, 2023).

What makes a good Expert Witness?

The most important thing that someone called up as an Expert Witness must remember is that their duty is to the court, not to the prosecution or the defense (COPFS, 2023). However, other important aspects of an Expert Witness make their testimony more reliable (Maggio, 2022).

Knowledge

Of course, they must know what they are talking about, but they must be confident enough in their knowledge without being arrogant.

Communication

An Expert Witness must be able to speak clearly on their subject, but also in a way that the jury feels informed, not talked over or blinded by science. They should be able to stay calm and consistent even under pressure. The Jury is looking not just for the information, but how the witness tells it.

No Speculation

A good Expert Witness speaks on information that is outside the experience of a judge or a jury, but will state clearly when a question is beyond the Witness’s expertise.

So what happens when an Expert Witness gets it wrong?

Case Studies

The textbook case for a poor expert witness is that of Sally Clark in the UK.

Misuse of Statistics in Court

1998. Sally Clark in the UK had the horror of two sons dying from Sudden Infant Death Syndrome (SIDS). Then she and her husband were arrested for murder because an Expert Witness presented statistical evidence that it was unlikely for two such deaths in the same family. While her husband was acquitted, Sally Clarke was imprisoned, until a different expert proved that it was more likely not less likely for the two deaths to be related. The first expert stated that there was a 1 in 73 million chance that the two boys had died of SIDS. What wasn’t presented in court was the assessment that there was a 1 in 2 billion chance that the two boys were murdered. Taking that into consideration it was 4% likely that the mother murdered the children, and something close to 95% likely that both children died of SIDS (Carriquiry, 2018).

Mis-match of Bite Marks

It’s 1987, and Steven Chaney has just been convicted of double murder, because a medical witness assured the judge and jury that a wax bite mark of Chaney’s mouth matched the bite on the arm of one of the victims. It wasn’t until 2015 that Chaney was released because scientific advancements found that the evidence used at the original trial was unsafe.

Image 3: A Drawing of a bite mark.
Credit: https://www.researchgate.net/figure/Images-shows-different-bite-marks-on-human-skins-and-fruits-in-different-crimes-as_fig4_260341872

A discussion regarding the re-evaluation of the evidence on bite marks can be found in this article.  While it is clear that bite mark evidence is unsound, courts have yet to declare such evidence inadmissible (Murphy, 2019).

Training for Expert Witness Status

Currently, there is no requirement for training for a role in court, such as that in the MSc Forensic Science course I took. Knowledge of the subject is vital to the role of Expert Witness, but it is clear from the above case studies that failing to present the information in a way that a jury can understand can lead to wrongful conviction or an inappropriate acquittal. To be an Expert Witness, the person must be able to communicate the necessary evidence clearly, and at a level that lay people find useful. It helps to know how a courtroom works and what the legal requirements are. With some training, expert testimony would lead to fewer miscarriages of justice (Burns, 2023).

Conclusion

The movie My Cousin Vinny is a regular teaching tool for Expert Witnesses, showing both how to and how not to give evidence in court. So where did I go wrong in presenting my evidence in a make-believe court case? I believe I was over-confident, and thought everyone should believe my evidence because I knew what I was doing. I’m grateful to that trainee lawyer for the lesson in humility, and for showing everyone what it takes to be an Expert Witness.

References

Burns, M. (2023). Expert Witnesses – training should be mandatory. RICS. May 30. https://www.rics.org/news-insights/expert-witnesses-training-should-be-mandatory#:~:text=It%20is%20possible%20that%20judges,not%20trained%20in%20the%20role.&text=Expert%20witnesses%20need%20to%20be,that%20the%20tribunal%20will%20understand

Carriquiry, A. (2018). Misuse of Statistics in the Courtroom: The Sally Clark Case. Centre for Statistics and Applications in Forensic Evidence.  February 16. https://forensicstats.org/blog/2018/02/16/misuse-statistics-courtroom-sally-clark-case/

COPFS. (2023). Expert Witness Guide. Crown Office and Procurator Fiscal Service. 16 Aug. https://www.copfs.gov.uk/for-professionals/expert-witness-guide/#:~:text=An%20expert%20or%20skilled%20witness,engineering

Guthrie, C.M (2007). One Witness, Two Hats, Three Cases. US Department of Justice. October. https://www.ojp.gov/ncjrs/virtual-library/abstracts/one-witness-two-hats-three-cases

Laney, C. & Loftus, E. F. (2023). Eyewitness testimony and memory biases. In R. Biswas-Diener & E. Diener (Eds), Noba textbook series: Psychology. Champaign, IL: DEF publishers. Retrieved from http://noba.to/uy49tm37

LII. Character Witness. Legal Information Institute. https://www.law.cornell.edu/wex/character_witness#:~:text=Under%20common%20law%2C%20the%20defendant,instances%20of%20the%20defendant%27s%20conduct

Maggio, E. (2022). 3 Traits Every Exceptional Expert Witness Possesses. Expert Institute. January 19. https://www.expertinstitute.com/resources/insights/for-experts-traits-of-exceptional-expert-witnesses/

Murphy, H. (2019). A Leading Cause of Wrongful Convictions: Experts Overstating Forensic Results.  New York Times. April 20. https://www.nytimes.com/2019/04/20/us/wrongful-convictions-forensic-results.html

Smith, F.C. and  Bace, R. G.,  Chapter 4: Examples of Expert Witnesses and their Communities of Interest.  A Guide to Forensic Testimony. Addison-Wesley. September 2002. https://books.google.co.uk/books?id=KmZqqM8nlaUC&pg=PA4&lpg=PA4&dq=movie+about+a+witness+for+the+defence+who+knows+about+tires&source=bl&ots=xfFSewQEib&sig=ACfU3U2d6xCxWOzL8NM0_hFlrRm1NslDPA&hl=en&sa=X&ved=2ahUKEwiN54rG7-iCAxUjoFwKHRECBiEQ6AF6BAgqEAM#v=onepage&q=movie%20about%20a%20witness%20for%20the%20defence%20who%20knows%20about%20tires&f=false