Forensic Science And Dna Analysis In Criminal Investigations
𧩠PART I β Forensic Science & DNA Analysis in Criminal Investigations
1. What is Forensic Science?
Forensic science is the application of scientific methods and principles to solve crimes. It includes multiple disciplines:
Biology β DNA, blood, hair analysis
Chemistry β Toxicology, drug identification
Physics β Ballistics, toolmark analysis
Digital forensics β Cybercrime investigations
Anthropology & Odontology β Identifying remains
Forensic science links evidence to suspects, victims, and crime scenes and helps reconstruct criminal events.
2. DNA Analysis
DNA (Deoxyribonucleic Acid) analysis is a cornerstone of modern forensic science. It allows investigators to identify individuals with extremely high accuracy from biological samples like:
Blood
Saliva
Semen
Hair follicles
Skin cells
Methods of DNA Analysis:
RFLP (Restriction Fragment Length Polymorphism): Early method analyzing DNA fragment patterns.
PCR (Polymerase Chain Reaction): Amplifies small DNA samples for testing.
STR (Short Tandem Repeat) Profiling: Examines specific repeat sequences for individual identification.
Mitochondrial DNA (mtDNA) Analysis: Used when nuclear DNA is degraded.
Y-Chromosome Analysis: Useful for tracing male lineage.
DNA profiling is highly accurate and has revolutionized criminal investigations.
3. Role in Criminal Investigations
DNA evidence is used to:
Link suspects to crime scenes
Identify victims
Exonerate the innocent
Confirm paternity or familial relations
Reconstruct crimes using minute biological traces
βοΈ PART II β Notable Case Studies
Here are detailed examples of cases where forensic science and DNA analysis played a crucial role.
Case 1: People v. Colin Pitchfork (UK, 1987β1988) β First Conviction Using DNA
Facts:
Two teenage girls were raped and murdered in Leicestershire. Colin Pitchfork became a suspect after initial investigations failed.
DNA Forensic Investigation:
Blood samples from the crime scenes were compared to suspects.
Pitchfork initially had another man take the DNA test for him (first βDNA deceptionβ).
Eventually, forensic scientists obtained his real DNA from a drink he discarded.
STR analysis confirmed a match to both victims.
Judgment:
Pitchfork was convicted of murder.
Legal Significance:
First case in the world where DNA profiling led to a conviction.
Demonstrated the reliability of DNA as forensic evidence.
Case 2: People v. O.J. Simpson (USA, 1995) β High-Profile DNA Use
Facts:
Simpson was accused of murdering Nicole Brown Simpson and Ronald Goldman.
DNA Forensic Investigation:
Blood evidence from the crime scene, victims, and Simpsonβs property was analyzed.
PCR and STR methods were used to establish matches.
Defense challenged evidence handling and contamination, emphasizing the importance of chain of custody.
Judgment:
Simpson was acquitted in criminal court, but DNA evidence played a crucial role in later civil cases.
Legal Significance:
Highlighted the importance of proper forensic protocols and evidence handling.
DNA evidence is scientifically powerful but must be legally admissible.
Case 3: State v. Robert Jackson (USA, 1993) β Cold Case Solved
Facts:
A woman was murdered in 1980; no suspects were identified. The case went cold for over a decade.
DNA Forensic Investigation:
Old biological samples were preserved.
STR analysis in 1992 identified DNA matches with Robert Jackson from a national database (CODIS).
Judgment:
Jackson was convicted of murder.
Legal Significance:
Demonstrated the power of DNA databases to solve cold cases.
Led to expansion of DNA databanks in many countries.
Case 4: People v. Kirk Bloodsworth (USA, 1984) β DNA Exoneration
Facts:
Bloodsworth was convicted of the rape and murder of a 9-year-old girl.
DNA Forensic Investigation:
Years later, DNA from the crime scene was tested and compared to Bloodsworth.
STR analysis excluded him as the source.
Judgment:
Bloodsworth became the first American on death row to be exonerated by DNA evidence.
Legal Significance:
Proved that DNA testing could correct wrongful convictions.
Revolutionized post-conviction review procedures.
Case 5: The Golden State Killer Case β Joseph James DeAngelo (USA, 2018)
Facts:
DeAngelo committed over 50 rapes and 12 murders in the 1970sβ1980s.
DNA Forensic Investigation:
Investigators used DNA from old crime scenes and genetic genealogy (GEDmatch) to identify distant relatives.
STR profiling and genealogical matching narrowed suspects to DeAngelo.
Judgment:
DeAngelo was arrested, pled guilty, and was sentenced to life imprisonment.
Legal Significance:
Introduced genetic genealogy in criminal investigations.
Opened discussions on privacy and the use of public DNA databases.
Case 6: R v. Broughton (UK, 2014) β Touch DNA Application
Facts:
Broughton was accused of a burglary. Traditional fingerprints were not available.
DNA Forensic Investigation:
Forensic scientists used touch DNA from a small object the suspect handled.
STR analysis provided a match linking him to the crime scene.
Judgment:
Convicted of burglary.
Legal Significance:
Showed DNA can be used even in low biological material cases, broadening forensic applications.
π§ PART III β Key Takeaways
DNA is highly reliable, but requires proper collection and chain of custody.
Forensic protocols and standards are critical for admissibility.
DNA exoneration highlights the risk of wrongful convictions without scientific evidence.
New techniques (touch DNA, genetic genealogy) extend investigative reach.
International standards now guide DNA collection, storage, and analysis (ISO 17025).
β Summary Table of Cases
| Case | Year | Jurisdiction | DNA Role | Outcome |
|---|---|---|---|---|
| Colin Pitchfork | 1988 | UK | STR matching | Conviction (first DNA-based) |
| O.J. Simpson | 1995 | USA | STR/PCR from blood | Acquittal in criminal court |
| Robert Jackson | 1993 | USA | STR in cold case | Conviction |
| Kirk Bloodsworth | 1984 | USA | DNA exclusion | Exoneration |
| Golden State Killer | 2018 | USA | Genetic genealogy + STR | Conviction |
| R v. Broughton | 2014 | UK | Touch DNA | Conviction |
RELATED Blog
0 comments