Maintaining the chain of custody: Anti-contamination measures for trace DNA evidence

Trace DNA evidence has become an essential tool in forensic investigations, but its reliability is dependent on strict adherence to protocols and procedures that ensure the integrity of the evidence is preserved throughout the investigation. Maintaining a clear chain of custody is critical to the admissibility of evidence in court, and its absence can result in the exclusion of evidence or even a mistrial being declared. Contamination is a significant issue when collecting DNA evidence at a crime scene, and anti-contamination measures must be taken to ensure the reliability and accuracy of the evidence. The use of technology, such as electronic chain of custody (eCOC), automated DNA extraction systems, real-time PCR analysis, DNA profiling software, and environmental monitoring systems, can enhance the accuracy and reliability of evidence. Law enforcement agencies and forensic labs must establish strict guidelines for the collection, preservation, and analysis of trace DNA evidence to maintain its integrity and admissibility in court.


Introduction
The use of trace DNA evidence has become an essential tool in forensic investigations, allowing investigators to identify suspects, exonerate the innocent, and solve crimes that would have otherwise gone unsolved [1].Trace or touch DNA is frequently found in minute quantities at crime scenes, and it is one of the most common types of DNA samples collected from crime scene exhibits.However, the process of touch DNA profiling can be impacted by many factors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], which can lead to low levels of DNA recovery.Furthermore, trace DNA can be single or mixed source, making the analysis much more complicated if it is exposed to contamination during the crime scene investigation and DNA profiling process.The reliability of trace DNA evidence is dependent on strict adherence to protocols and procedures that ensure the integrity of the evidence is preserved throughout the investigation [17].One crucial aspect of maintaining the integrity of trace DNA evidence is the chain of custody, which refers to the documentation and tracking of evidence from the moment it is collected to the point of its presentation in court.
The chain of custody is essential in establishing the authenticity and integrity of trace DNA evidence, and it provides a means of verifying that the evidence has not been tampered with or contaminated [18].It requires strict adherence to procedures and protocols, including proper documentation of the collection and transfer of evidence, and the use of appropriate packaging and labelling [19].Maintaining a clear chain of custody requires the cooperation of all parties involved in the investigation, including law enforcement officials, forensic scientists, and attorneys.
A clear chain of custody is critical to the admissibility of evidence in court, and its absence can result in the exclusion of evidence from trial or even a mistrial being declared [20].In the case of trace DNA evidence, the chain of custody is especially important due to the risk of contamination from environmental sources, such as dust, debris, or even the investigators themselves [21].The failure to maintain a clear chain of custody or prevent contamination can have significant consequences, including the inability to use evidence in court or even the wrongful conviction of an innocent person.
In the following sections, we will discuss the sources of contamination in trace DNA evidence and how to avoid them, anti-contamination measures at crime scenes, chain of custody protocols and documentation, the role of technology in maintaining the chain of custody, and the importance of these measures in preserving the integrity of trace DNA evidence.

Sources of contamination in trace DNA evidence and how to avoid them
Trace DNA evidence can be incredibly valuable in criminal investigations, but it's also highly susceptible to contamination.Contamination can occur at any stage of the collection, handling, and analysis process, and can compromise the reliability and accuracy of the results.Therefore, it's important to be aware of the potential sources of contamination and take steps to minimize them.The primary source of contamination is the handling of samples by individuals.DNA can be transferred from skin cells, hair, sweat, and saliva, among other sources, and can contaminate a sample [22].To avoid human contamination, all individuals who handle DNA samples should wear gloves, masks, and other protective equipment to reduce the chance of transferring their DNA onto the sample.Additionally, samples should be collected and stored in a way that minimizes the chance of contact with human DNA.
Trace DNA can also be contaminated by environmental factors such as dust, dirt, and other biological materials [23].These contaminants can be introduced at any stage of the collection and analysis process, including during the transportation and storage of samples.To avoid environmental contamination, samples should be collected in a sterile environment, using clean and properly sterilized collection tools.Samples should also be stored in airtight containers in a controlled environment to prevent exposure to environmental contaminants.
Cross-contamination can occur when DNA from one sample is transferred to another sample during the collection, handling, or analysis process [24].This can happen when samples are processed in the same laboratory or when contaminated equipment is used.To avoid cross-contamination, strict protocols should be in place for the handling of samples and equipment, and samples should be processed one at a time to prevent cross-contamination.
DNA can also be contaminated by the equipment used in the collection and analysis process [25].This can happen when the equipment is not properly cleaned and sterilized or when the same equipment is used for multiple samples.To avoid equipment contamination, all equipment should be properly sterilized and cleaned between samples, and disposable equipment should be used whenever possible.
Sample mix-ups can occur when samples are mislabelled or incorrectly identified, leading to inaccurate results [26].To avoid sample mix-ups, strict protocols should be in place for sample labelling and tracking, and samples should be identified and tracked throughout the entire collection and analysis process.

Anti-contamination measures at crime scenes: best practices for trace DNA evidence collection
Contamination can be a significant issue when collecting DNA evidence at a crime scene.To ensure the reliability and accuracy of the evidence, it's crucial to take anti-contamination measures.These measures can help to prevent the transfer of DNA from one location to another, minimize the risk of human contamination, and avoid environmental contamination.Here are some anti-contamination measures that can be taken at a crime scene  Wear protective clothing [27]: Crime scene investigators should wear protective clothing, including gloves, masks, and disposable coveralls to prevent the transfer of their own DNA onto the evidence.The clothing should be changed frequently to avoid cross-contamination between different areas of the crime scene. Use clean collection tools [28]: Crime scene investigators should use clean and sterilized collection tools to avoid contamination of the evidence.These tools should be cleaned between each use, and disposable tools should be used whenever possible.
 Collect evidence in a systematic manner [29]: Crime scene investigators should collect evidence in a systematic manner, starting from the furthest point from the entrance and working towards the exit.This helps to avoid contamination of evidence by investigators moving through the scene. Minimize movement [30]: Crime scene investigators should minimize their movement within the crime scene to reduce the risk of contamination.This includes avoiding unnecessary movement and limiting the number of investigators present at the scene. Use protective packaging [31]: Evidence should be packaged in protective containers, such as paper bags or airtight containers, to prevent contamination by environmental factors such as dust and moisture.The packaging should be labelled clearly and stored in a secure location to avoid tampering.

Ensuring the integrity of trace DNA evidence: chain of custody protocols and documentation
Ensuring the integrity of trace DNA evidence is essential to maintaining the chain of custody, which is the chronological documentation of the handling, transfer, and custody of evidence.Chain of custody protocols and documentation are crucial to ensure the admissibility and reliability of trace DNA evidence in court.Here are some key points to consider when implementing chain of custody protocols and documentation for trace DNA evidence:  Documentation of evidence collection [32]: The chain of custody begins with documentation of the evidence collection process.This documentation should include the date and time of collection, the location of the evidence, the name of the collector, and any other relevant information about the collection process. Proper labelling and packaging of evidence [29]: Proper labelling and packaging of evidence is crucial to maintaining the integrity of the evidence.Evidence should be labelled with a unique identifier, such as a case number or evidence number, and packaged in a way that prevents contamination and ensures preservation of the DNA. Documentation of evidence storage and handling [32]: Any time evidence is transferred or handled, it should be documented in the chain of custody.This includes documentation of the date and time of transfer, the identity of the person who transferred the evidence, and the reason for the transfer. Controlled access to evidence [31]: Access to evidence should be controlled and limited to authorized personnel.Access should be documented in the chain of custody, including the name of the person accessing the evidence, the date and time of access, and the reason for the access. Documentation of evidence analysis [33]: The analysis of trace DNA evidence should be carefully documented in the chain of custody, including the date and time of analysis, the name of the analyst, and the methods used for analysis. Storage of evidence [34]: Evidence should be stored in a secure location that is designated for evidence storage.
The storage location should be documented in the chain of custody, along with the name of the person responsible for the storage and the date and time of storage.

The role of technology in maintaining the chain of custody and preventing contamination in trace DNA evidence
As forensic technology advances, the role of technology in maintaining the chain of custody and preventing contamination in trace DNA evidence has become increasingly important.Examples of key technologies and their roles in ensuring the integrity of trace DNA evidence include electronic chain of custody (eCOC), automated DNA extraction systems, real-time polymerase chain reaction (PCR) analysis, DNA profiling software, and environmental monitoring systems.
One technology that can assist investigators in maintaining the integrity of the chain of custody is the electronic chain of custody (eCOC) system, which uses electronic documentation to track the movement and handling of evidence, from collection to analysis, creating a permanent, tamper-proof record of evidence handling [35].Additionally, the risk of contamination during the DNA extraction process can be minimized by using automated DNA extraction systems, which reduce the need for manual handling of samples and provide a standardized extraction process that improves the reproducibility of results [36].
Real-time polymerase chain reaction (PCR) analysis is a technology that allows for rapid and sensitive detection of DNA, thereby reducing the risk of contamination and degradation during the analysis process [37].This technology also enables the quantification of DNA, which can be useful in assessing the quality and quantity of DNA in trace samples.Additionally, DNA profiling software plays a crucial role in the interpretation of DNA profiles, ensuring the accuracy and reliability of the results, and helping to detect contamination or errors in the analysis process [38].
Finally, environmental monitoring systems, including air filtration systems and ultraviolet (UV) lights, can effectively prevent contamination in the laboratory by reducing the presence of airborne DNA and other contaminants [39].

Conclusion
In conclusion, proper collection, storage, and handling of trace DNA evidence are critical components of maintaining the integrity of evidence in criminal investigations.Effective anti-contamination measures must be implemented, such as maintaining a sterile environment, avoiding human contact, and using appropriate storage and transportation methods.Additionally, proper training, education, and protocols must be in place to ensure compliance with standard operating procedures and best practices for evidence handling and analysis.
Chain of custody protocols and documentation are essential in maintaining the integrity of evidence from the time of collection to presentation in court.The use of technology, such as electronic chain of custody (eCOC), automated DNA extraction systems, real-time PCR analysis, DNA profiling software, and environmental monitoring systems, can enhance the accuracy and reliability of evidence.
To maintain the integrity of trace DNA evidence, it is important to implement a comprehensive approach that combines the use of technology with effective anti-contamination measures, proper training, standard operating procedures, and best practices for evidence handling and analysis.This approach is necessary to ensure that the evidence collected at the crime scene is handled, processed, and stored in a way that maintains its integrity and admissibility in court.
Law enforcement agencies and forensic labs must establish strict guidelines for the collection, preservation, and analysis of trace DNA evidence.This will help maintain the integrity of the evidence and ensure its admissibility in court, ultimately contributing to the successful investigation and prosecution of criminal cases.