Reassessing the Forensic Evidence on Bite Marks

Science is not static, new information allows scientists to re-evaluate understood hypotheses, so no one would expect Forensic Science to stay still either. Each type of evidence needs constant evaluation to ensure that it still meets the criteria for a Court of Law, or whether it has become junk science. Working on this is a New York-based agency, the Innocence Project. They have used DNA evidence to clear the names of many wrongly convicted individuals. Now, they are working to clear the name of Charles McCrory, who was convicted of his wife’s murder based on bite marks. The Innocence Project is convinced that McCrory was wrongfully convicted on flimsy grounds (Pilkington, 2022). So is it time for reassessing forensic evidence on bite marks?

What are the Criteria for Evidence admissibility in a Court of Law?

For evidence to be admissible in a court of law it must pass three tests.

Is it Relevant?

Relevancy means will it tend to prove or disprove the innocence of the defendant.

Is it Material?

For evidence to be considered material, it must be entered as evidence to prop up a disputed fact under discussion.

Is it Competent?

Competency is a less reliable standard. It generally refers to how well the evidence compares with traditions and precedents of previous trials. This is gradually being phased out (Findlaw Team, 2019).

Criteria for Scientific Evidence to be admissible in a Court of Law

Scientific evidence in the USA is additionally judged under the Daubert Standard. As mentioned in last month’s article on proteomics, this has a further five levels on top of the previous three tests (Legal Information Institute, 2022).

1. Has the methodology been tested?
2. Has there been a publication and peer review of the methodology?
3. What is the error rate of the methodology?
4. Are there standards in place to validate the methodology?
5. Has the wider scientific community accepted the methodology?

When reassessing forensic evidence all of these criteria must be considered.

What is Junk Science?

According to Chris Fabricant in his book Junk Science and the American Justice System, Junk Science is ‘subject speculation masquerading as an Expert Opinion’ (Pilkington, 2022). It looks like science but the methodology does not stand up to peer review nor do the standards appear to validate it.

How are Bite Marks currently analyzed as Evidence?

Image 1: How to analyse a bite mark.

Bite marks are analyzed by a Forensic Dentist. When the bite mark is on a living person, a Forensic Dentist must see the mark as soon as possible, because all injuries change as they heal. Or, if the mark injury is on a dead body, the decay process may also cause changes to the evidence. So, the examination by the Forensic Dentist must cover these points (Freeman, 2022).

1. Is the bite from a human or an animal? — The pattern of the teeth impressions varies depending on the source.
2. Swab the wound for saliva — this may provide DNA. It is not unheard of for a person to bite themselves while attempting to incriminate someone else.
3. Measure the wound and use photographs to record it — with the changing nature of the mark, taking a series of pictures over several hours is vital.
4. For a deceased individual, the bite mark may be cut off the body and preserved in formalin. Casts can then be taken of the mark in silicone.

When the investigator has a potential suspect in custody, then a cast may be made of the suspect’s teeth, in an attempt to match the cast of the victim’s mark (Bite Marks, 2022).

Where are bite marks found?

Image 2: a dog bite

Not only can bite marks be observed on the skin but they can also be found on other items, such as an apple left at the scene. It is not only murder victims found with bite marks. Victims of sexual assault can be bitten. For a woman, this is often on the breasts or legs. If the victim was in a position to fight, bite marks might be discovered on the attacker’s face and arms (Claridge, 2023).

Describing a bite mark

In their contemporaneous notes, the Forensic Dentist can describe the mark in many different ways. Each of the teeth leaves its own impression. Crooked and missing teeth make a distinct pattern, and the strength of the jaw can affect the depth of the mark (Claridge, 2023).

There are specific ways of recording the mark. An Abrasion is a slight scrape, whereas an Artifact describes when a piece of the body, such as an ear, has been bitten off. If the dentist records a Noticeable impression that means aggressive force was used to inflict the injury (Freeman, 2022). See the infographic in the title picture above for the full list.

All of these observations depend on the subjective opinion of the Forensic Dentist (Bite Mark Evidence, 2023).

Photographing Bite Marks for Forensic Evidence

A simple photograph does not give reliable evidence of a bite mark. The injuries are often on a curved surface so that the parts closer to the camera are magnified. A special scale is used for these injuries. A circle crossed by lines on an ABFO scale no2, allows the viewer to see any distortions. If the lines in the circle are anything other than straight, then the photographs need to be taken again. It you wish to know more about the distortion ing photographing bite marks, check out this video.

Image 3: The ABFO no2 scale helps show the distortion in bite marks.

A photograph needs to be taken immediately before the wound becomes inflamed or that will cause further distortion (Bassed). These distortions make it difficult or impossible to match a bite mark to a cast of a potential suspect.

A Case Study for Reassessing the Evidence on Bite Marks

As I mentioned in the introduction, Charles McCrory was convicted of the murder of his wife on bite mark evidence.

The founder of the science of Bite Mark Analysis, Richard Souviron, testified against McCrory at the initial trial. Instead of the usual statements of possibility, Souviron stated that the bite marks were definitely made by McCrory. Before the trial, Souviron had stated the injuries might be bite marks but provided insufficient evidence for identification. According to the book, Junk Science and the American Justice System, previous to Souviron an investigator would see bite marks and find an expert to prop up his theory on the identity of the perpetrator (Pilkington, 2022).

Cases like this one, and the 1992 case of Ray Krone, who was released after DNA evidence proved the bite mark was not his, are the reason the Innocence Project is pushing for a reassessment of forensic evidence for bite marks (Bite Mark Evidence, 2023).

Do Bite Marks reach the Daubert Standard?

Bite mark analysis became accepted when serial killer Ted Bundy was convicted in 1979 (Taylor& Francis, 2023). However, in 2022, the National Institute of Standards and Technology issued a draft statement on a review of Forensic Bite Mark Analysis. The draft indicates that Bite Mark analysis failed to meet the standards of reliability, accuracy, and validity. Contrary to the opinion of Forensic Dentists such as Richard Souviron, patterns of teeth are not individual in the same way as fingerprints or DNA. It goes on to report that a single person can make different bite mark patterns, such that individual patterns cannot be attributed to any one person.

So this new report suggests that Forensic Bite Mark Analysis does not reach the criteria necessary for admissibility in a Court of Law. The draft report was opened for comments, which were taken into consideration for the Final Report (NIST, 2022). In June 2023, the final report states clearly that bite marks are not reliable evidence for conviction (Taylor& Francis, 2023).

In Conclusion

Forensic Science is by definition the application of the scientific method to evidence submitted to a Court of Law. When new information arrives, it must be taken under consideration, and beliefs and theories must change if the additional information proves valid. With the new facts, the experts involved in Reassessing the Forensic Evidence for Bite Marks have concluded that bite mark analysis is no longer valid. The Innocence Project will have a strong case for proving that individuals convicted on the evidence of bite marks are Not Guilty.

Image

https://www.researchgate.net/figure/Images-shows-different-bite-marks-on-human-skins-and-fruits-in-different-crimes-as_fig4_260341872

References

Bassed, R. & Tarvardi, P. Photography of Bite Marks. Future Learn. Bite Marks. (2022) Crime Museum. https://www.crimemuseum.org/crime-library/forensic-investigation/bite-marks/

Bite Marks. (2022) Crime Museum. https://www.crimemuseum.org/crime-library/forensic-investigation/bite-marks/

Bite Mark Evidence. (2023) The California Innocence Project. https://californiainnocenceproject.org/issues-we-face/bite-mark-evidence/#:~:text=Bite%20mark%20evidence%2C%20an%20aspect,the%20dental%20impressions%20of%20suspects.

Claridge, J. (2023) Bite Marks. Explore Forensics. https://www.exploreforensics.co.uk/bite-marks.html

Findlaw Team. (2019) Evidence: The Concept of Admissibility.  Findlaw. March 20. https://www.findlaw.com/criminal/criminal-procedure/evidence-the-concept-of-admissibility.html

Freeman, S & McManus, M.R. (2022) How Forensic Dentistry Works. How Stuff Works. Jan 27. https://science.howstuffworks.com/forensic-dentistry3.htm

Legal Information Institute. (2022). Daubert Standard. Cornell Law School. https://www.law.cornell.edu/wex/daubert_standard#:~:text=The%20Daubert%20standard%20is%20the,to%20the%20facts%20at%20issue

NIST. (2022) Forensic Bitemark Analysis  Not Supported by Sufficient Data, NIST Draft Review Finds. October 11. NIST.  https://www.nist.gov/news-events/news/2022/10/forensic-bitemark-analysis-not-supported-sufficient-data-nist-draft-review

Pilkington, E. (2022) A Bite Mark, a Forensic Dentist, a Murder: How Junk Science Ruins Innocent Lives. The Guardian. April 28. https://www.theguardian.com/us-news/2022/apr/28/forensics-bite-mark-junk-science-charles-mccrory-chris-fabricant

Taylor& Francis. (2023) Forensic Bitemark Analysis for Court Trials is not Supported by Sufficient Data and “is leading to wrongful convictions”. June 23. Taylor&Francis: An informa business. https://newsroom.taylorandfrancisgroup.com/forensic-bitemark-analysis-for-court-trials-is-not-supported-by-sufficient-data-and-is-leading-to-wrongful-convictions/