DNA analysis plays a pivotal role in identifying perpetrators and strengthening evidence in criminal cases; DNA analysis is frequently used in cases involving sex crimes, murder, robbery, and assault because it analyzes genetic information to identify a person and is considered highly reliable as evidence. Below is a detailed description of DNA testing in criminal cases.
Purpose of DNA Analysis
The main purposes of DNA testing in criminal cases are
- Identification of the cul prit: DNA analysis of blood, body fluids, skin fragments, hair, nails, saliva, etc. left at the crime scene is used to identify the culprit.
- Suspect Exclusion: If the suspect’s DNA does not match that left at the crime scene, he or she may be proven innocent.
- Victim Identification: The DNA of the victim is analyzed to confirm the victim’s identity. Used especially when unidentified bodies are found.
- Identification of the involved parties: If more than one person was involved, it is possible to identify each of the involved parties by matching multiple DNA samples left at the crime scene.
2. The DNA analysis process
DNA testing in criminal cases is performed in the following steps
(1) Sample collection
- On-site DNA collection: DNA samples are collected from blood, body fluids, hair, saliva, and other evidence left at the crime scene. This includes blood on floors and furniture, as well as on clothing and tools.
- DNA collection from suspects and victims: DNA is collected from suspects and victims from their oral mucosa or blood and matched with samples from the crime scene.
(2) DNA extraction and amplification
DNA is extracted from the collected sample and the DNA is amplified using PCR (polymerase chain reaction) technology to the amount needed for analysis.
(3) Genotype analysis
The amplified DNA samples are analyzed for specific genotypes (STR markers).This creates a DNA profile specific to the individual.
(4) DNA profile matching
The DNA profile created is matched with DNA samples from the crime scene. It may also be compared with DNA from past criminals or unsolved cases registered in police DNA databases (e.g., “D-File” in Japan).
Examples of crimes for which DNA testing is used
- Murder: Blood and body fluids left at the murder scene, as well as DNA from objects touched by the murderer, are important clues for identifying the murderer.
- Sex crimes: the DNA of the perpetrator is typically collected from the victim’s body, clothing, or other physical evidence to confirm a match with the suspect.
- Robbery: The perpetrator is identified based on DNA found in the perpetrator’s blood, skin fragments, or tools left behind during the crime.
- Assault cases: DNA on the victim or assailant will identify what kind of contact was made, and the details of the incident will be revealed.
4. Reliability of DNA testing
DNA testing is powerful evidence in criminal cases because it can identify individuals with a very high degree of accuracy. The possibility of misidentification is very low, and theoretically the probability of two people having identical DNA profiles is extremely small. However, proper sample collection and storage is important to ensure the reliability of the results of the analysis.
5. Limitations of DNA testing
- Sample contamination: If DNA samples are contaminated or mixed, accurate results may not be obtained.Also, if multiple DNA samples are present at the same site, work must be done to separate them!
- It can take time: While urgent cases can yield results quickly, complex cases or large sample sizes can take weeks or months before results are available.
- Difficulty of interpretation: It can be difficult to determine which DNA belongs to whom, especially in cases involving more than one person. Analysis and interpretation by appropriate experts is required.
6. DNA database
The police use DNA databases for criminal investigations.This includes DNA information from previously arrested criminals and unsolved cases.If a DNA sample taken in a new case matches the information in the database, it is more likely that a suspect will be identified.
Legal Aspects of DNA Testing
DNA analysis is very powerful as evidence in court.However, when the results of the analysis are used in court, the sample collection and storage procedures must be strictly followed.Improper handling may result in the sample not being adopted as evidence.
summary
DNA analysis is an extremely powerful tool in criminal investigations and identification of perpetrators. Especially in serious cases, analysis of DNA left at the crime scene can greatly contribute to identifying the perpetrator and proving innocence. Proper handling of samples and rigorous analysis are necessary for the results of the analysis to be reliable. DNA analysis results are also important in legal proceedings, but it is important that the sample handling methods and the accuracy of the results as evidence are ensured.
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Supervisor of the article
Dr. Hiroshi Oka
Graduated from Keio University, Faculty of Medicine
Doctor of Medicine
Medical Doctor
