Touch DNA: A Double- Edged Sword in Criminal Justice

 Author: REVATHI G S, MSc Forensic Science

Introduction

DNA is one of the most reliable methods for individualisation. For decades, DNA has beenu tilised by forensic experts as corroborated evidence in case solving. 

Scientists are able to create profiles from quantities as little as nanograms thanks to the growing improvements and increased sophistication of the tools used in DNA analysis. 

Samples of blood, semen, saliva, vomit, and other bodily fluids can all contain DNA. The little quantities of DNA that remain on things after they are touched are referred to as touch DNA. 

In forensic investigations, this kind of DNA evidence can be extremely valuable since it enables the identification of people who may have handled or come into contact with an object, even for a short time. Touch DNA may typically be used to create a DNA profile from a small number of skin cells. 

This is a very little amount of DNA, often less than 100 picograms.

Shedder status, surface type, pressure of contact, and the technique utilised for DNA collection and extraction are among the various factors that influence the effectiveness of generating a significant quality DNA profile from Touch DNA. There are certain gaps in the published data on touch DNA recovery, despite the fact that earlier research has examined the efficacy of several DNA recovery techniques. In order to assess how successful touch DNA sampling is, it is crucial to consider the length of time the deposit remains on the surface as well as the area that is touched.

Collection and analysis of touch DNA

Different techniques can be used for the collection of touch DNA for criminal investigations.

Some of them are:

1. Collection using swabs

2. By using adhesive tape

3. Methods which are designed to pickup tiny skin cells from surfaces

Surfaces from which touch DNA can be collected includes:

1. Clothing

2. Weapons

3. Door handles

4. Paper etc

Contamination should be avoided by taking care during collection, as the small amount of DNA can be easily swamped by DNA from other sources.

Analysis can be done by various steps:

1. Extraction: DNA can be extracted from the collection in a laboratory setting PCR amplification: 

2.The extracted DNA is then amplified from the small amount to generate a profile.

3. Profiling: The amplified DNA is then analysed in specific regions that are known to vary between individuals.

Applications of touch DNA

1. Touch DNA can be used to link suspects to crime scene or objects found at crime scenes like weapons or stolen items.

2. It is also instrumental in solving cold cases where usual and traditional forms of evidence are not available.

3. Touch DNA evidence has been used to exonerate individuals who were wrongfully convicted.

Challenges in using touch DNA as evidence to solve crimes

1. Small amount of DNA can be sometimes insufficient for analysis, leading to partial or inconclusive results.

2. Environmental factors such as heat, moisture and UV light can degrade DNA making it more difficult to obtain a clear profile.

3. Objects touched by multiple people can contain a mixture of DNA from different individuals, complicating the analysis.

Conclusion

Touch DNA is valuable but delicate form of forensic evidence that requires careful collection and sophisticated analysis to be effective in criminal investigations. This article contains the importance of touch DNA in criminal investigations, its collection, analysis, challenges and applications.

References

1. A review on touch DNA collection, extraction, amplification, analysis and determination of phenotype panel. Pratiksha H. Nimbkar, Vaibhav D. Bhatt

2. The Affecting Factors of Touch DNA

Alketbi, Salem Khalifa (2018) The Affecting Factors of Touch DNA. Journal of Forensic Research, 9 (3). pp. 1-4. ISSN 2157-7145

3. Evaluation of tapelifting as a collection method for touch DNA Timothy J. Verdon (ab), R. John Mitchell(b), Roland A.H. van Oorschot(a)