Genetic Testing

DNA Analysis in Criminal Cases

親子鑑定　NIPPT　DNA鑑定　刑事事件

↓今すぐDNA出生前親子鑑定を予約する↓

簡単WEB予約はこちら

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.

医師監修 監修日：2024年9月17日

岡 博史 （おか ひろし）

医師・医学博士 ／ ヒロクリニック統括院長

YouTubeチャンネルなどを通じて、遺伝子やNIPT（新型出生前診断）についてわかりやすく発信しています。

略歴

  • 1996年 慶應義塾大学医学部 卒業
  • 2004年 慶應義塾大学 医学博士号 取得
  • 2005年 慶應義塾大学 皮膚科学教室 助手
  • 2008年 ヒロ皮フ形成クリニック 開業
  • 2009年 医療法人社団福美会 理事長
  • 2015年 医療法人社団福美会 理事

資格・所属

  • CAPラボディレクター
  • 日本皮膚科学会 皮膚科専門医
  • 日本医師会 産業医
  • 東京衛生検査所 指導監督医

発信・関連リンク

この記事は、 ヒロクリニックNIPPTの編集・監修体制 にもとづき、資格を持つ医師が内容を確認しています。

医師監修 監修日：2024年9月17日

堤 修一 （つつみ しゅういち）

医師・医学博士 ／ ヒロクリニック博多駅前院 院長

略歴

  • 1993年 東京大学医学部医学科 卒業
  • 2016〜2019年 東京大学先端科学技術研究センター 准教授

発信・関連リンク

この記事は、 ヒロクリニックNIPPTの編集・監修体制 にもとづき、資格を持つ医師が内容を確認しています。

参考文献

  1. Jeffreys AJ, Wilson V, Thein SL. Individual-specific 'fingerprints' of human DNA. Nature. 1985 Jul 4;316(6023):76-9.
  2. Gill P, Jeffreys AJ, Werrett DJ. Forensic application of DNA 'fingerprints'. Nature. 1985 Dec 12;318(6046):577-9.
  3. Saiki RK, Scharf S, Faloona F, Mullis KB, Horn GT, Erlich HA, Arnheim N. Enzymatic amplification of beta-globin genomic sequences and restriction site analysis for diagnosis of sickle cell anemia. Science. 1985 Dec 20;230(4732):1350-4.
  4. Butler JM. Forensic DNA Typing: Biology, Technology, and Genetics of STR Markers. 2nd ed. San Diego: Academic Press; 2005.
  5. Jobling MA, Gill P. Encoded evidence: DNA in forensic analysis. Nat Rev Genet. 2004 Oct;5(10):739-51.

Latest Articles

Supervisor of the article

Dr. Hiroshi Oka

Director of CAP Laboratory

Graduated from Keio University, Faculty of Medicine

Doctor of Medicine

Medical Doctor