Bitemarks | How Forensic Investigators collect Bitemark evidence from body!

Collection of bitemarks should be done with its utmost precision. Photography, Swabbing, Casting and Lifting, are highly recommended techniques to collect it.

FORENSIC SCIENCEFORENSIC ODONTOLOGY

Shubham Kumar

1/29/20245 min read

Bitemarks are distinctive patterns or impressions left on an object or living tissue by an animal or human who used their teeth to bite that object or living tissue. They are recognized and seen as a form of physical evidence in various fields of forensic science, including forensic investigations, anthropology, odontology, and forensic wildlife.

The analysis and examination of bite marks are very crucial because it holds potential information about the identity of the biter. In order to deliver the proper justice to the victim, collection of bitemarks should be done with its utmost precision. Methods like Photography, Swabbing, Casting and Lifting, are highly recommended techniques to collect bitemarks.

Collection of bitemarks: All you need to know about the Photography, Swabbing Method, Casting and Impression Method and Lifting Method

This informative blog includes the information required to understand the "Techniques used in collection of bitemarks.". Please read it with patience.

Photography Method | Bitemarks Collection Technique

In forensic odontology, the collection of bite marks using photography methods is a crucial step in the investigation process. Photography allows for the direct comparison of bite marks with the model of suspects, which is specially created for analysis.

To ensure accurate and detailed documentation, the following guidelines and techniques are employed:

1. Perpendicular Photography

2. North Direction Marker

3. Optimal Lighting Arrangement

4. Use of Filters

5. High-Pixel Photography

6. Stereoscopic Photography

7. Ultraviolet (UV) and Infrared (IR) Photography

8. Inclusion of ABFO Numbers

9. Comprehensive Coverage

10. Capturing 3D and 2D Nature

Swabbing Method | Bitemarks Collection Technique

The collection of bite marks in forensic odontology is a critical process in obtaining valuable evidence. Bitemarks may contain traces of the assailant's saliva, which can serve as crucial DNA evidence. Although saliva is often not visible on the bite marks and may be dried up, Edmond Locard's principle "Every contact leaves a trace" suggests that some amount of trace evidence is left behind. The swabbing method is employed to collect saliva or traces of saliva present in the bite marks for further analysis and DNA profiling.

The swabbing method encompasses two primary techniques:

Single Swabbing Method

In the single swabbing method, a cotton swab is used to collect the saliva present in the bite marks. The average amount of saliva in bite marks is around 0.3 ml, which is spread over an area of approximately 20 cm. The swabbing should be done immediately after the bite is inflicted but before the mark is washed or disturbed. If it is determined that the bite marks were inflicted through cloth, the cloth itself may be taken as evidence. This process aims to capture DNA evidence present in the saliva.

After swabbing the bite marks, the cotton swab is allowed to dry, and then it is placed in a sealed plastic bag to prevent contamination or tampering. The swab is then sent to the laboratory for analysis, where DNA profiling and comparison can be conducted to link the saliva to potential suspects.

Double Swabbing Method

The double swabbing method is more detailed and involves two steps to collect saliva evidence. In this method, the cotton swab is first moistened with distilled water. It is then swabbed in the area where the contact of lips and tongue has been made. This is typically applied when little pressure is applied through the lips or tongue, leaving dried saliva evidence without significant bite marks.

The first swab is allowed to sun-dry at room temperature for approximately 45 minutes. Afterward, a second swab is imposed on the inflicted area to collect any remaining saliva evidence. This swab is also sun-dried at room temperature for about 45 minutes. The two swabs with collected saliva evidence are then sent to the laboratory for examination and analysis, ensuring the integrity of the evidence.

To maintain the integrity of the evidence, the swabbed cotton is sealed in plastic bags and stored in a cool environment to prevent bacterial contamination or degradation of the DNA evidence.

In cases of sexual assault, additional swabs may be taken, such as an oral swab or mouthwash, to detect the presence of semen.

Casting and Impression Method | Bitemarks Collection Technique

The casting and impression method involves creating a three-dimensional replica of the bite mark. The process begins with thoroughly cleaning and disinfecting the area around the bite mark, to prevent contamination and ensure the integrity of the evidence. Next, a mold or impression material is carefully applied to the bite mark site.

Rubber base and silicone-based materials have become popular choices due to their superior properties. Furthermore, their excellent stability, flexibility and non-water-soluble properties weaken the risk of degradation of saliva as evidence.

The mold is allowed to set and harden, capturing the precise contours and characteristics of the bite mark. Once solidified, the impression can be carefully removed from the skin. This process ensures that the three-dimensional replica accurately represents the original bite mark.

The further analysis involves, comparing the bite mark impressions with dental models obtained from suspects to identify potential matches.

Lifting Method | Bitemarks Collection Technique

In the lifting method, the use of polyvinylsiloxane (PVS) impression material in combination with plastic stock trays is highly recommended for efficient and accurate collection. PVS is a versatile dental impression material known for its stability and precision in capturing intricate details.

Fingerprint lifting powders are fine, colored powders that adhere to the surface of the bite mark, making the details more visible. A thin layer of fingerprint lifting powder is gently applied to the bite mark, and the excess is carefully removed to reveal the impression more clearly.

Fingerprint lifting tapes are then delicately pressed onto the powdered bite mark to lift the impression. These tapes have an adhesive side that adheres to the powder, ensuring that the impression is accurately transferred onto the tape's surface.

Once the impression is successfully lifted, it is preserved and secured for further examination and analysis. The lifted impression may be photographed to create a permanent record of the evidence.

In Case of Deceased Victim

However, that's not same in the case of deceased victim. Sometimes, the penetration of bitemarks reaches the underlying tissues. Moreover, the bitemarks are prone to get distorted due to decaying process. Therefore, acrylic is sprayed on the area surrounding the bite mark to prevent shrinkage and maintain the integrity of the impression. Furthermore, the use of special tools like plastic stock tray is used to collect the bitemark specimen. The polyvinylsiloxane (PVS) impression material is mixed and applied to the bite mark site, capturing all the intricate details of the bite.

After the impression is collected, it is carefully removed and preserved in a solution of 4% formalin mixed with formaldehyde. This solution helps maintain the structure and integrity of the bite mark, ensuring that it remains suitable for further examination and analysis.

This blog contains valuable insights as per the requirements of skills by Forensic Science Laboratories, we aim to provide a collective and informative knowledge to other viewers so that they can understand Techniques to collect the bitemarks from the crime scene, these techniques includes Photography method, Casting and Impression Method, Lifting Method and Swabbing Method.

Reference

  • "Forensic DNA Typing" by John M. Butler

  • "The Forensic Casebook: The Science of Crime Scene Investigation" by Ngaire E. Genge

  • "Forensic Science: A Very Short Introduction" by Jim Fraser

  • "Practical Crime Scene Processing and Investigation" by Ross M. Gardner