DNA Analysis and Case of DPP v Michael O'Callaghan

DNA profiling was discovered by Sir Alex Jeffreys in the 1980s in the UK.
Considered a crucial advancement in crime investigation, comparable to fingerprinting (Jim Fraser, 2010).
Led to the establishment of a DNA database in the Republic of Ireland (Criminal Justice (Forensic Evidence and DNA Database Systems) Act 2014).
DNA profiles can be used to include or exclude individuals in criminal or missing persons cases.
Overview of DNA analysis importance and its role in police investigations.

DNA (Deoxyribonucleic Acid):
- Genetic material of most living organisms.
- Nuclear DNA found in chromosomes in cell nuclei.
Types of DNA:
- Nuclear DNA: Main genetic material, present in all body cells except red blood cells.
- Mitochondrial DNA: Found in mitochondria, useful in identifying remains (e.g., Tuam Mother and Baby Home).
DNA Structure:
- Composed of two complementary strands forming a double helix (resembles a twisted ladder).
- Molecules of sugar (deoxyribose) and phosphate link nucleotides (A, T, G, C).
- Human genome consists of 22 pairs of chromosomes and sex chromosomes, housing all genetic material.
Genes and Alleles:
- Genes define heredity, made of two alleles (one from each parent).
- 25% of nuclear DNA is involved in gene expression; 75% is non-coding (junk DNA).
- Non-coding DNA contains repetitive sequences such as Short Tandem Repeats (STRs) which are significant for DNA analysis.

Steps in DNA extraction and analysis:
- Extraction: Method varies by tissue type; epithelial cells are easier compared to bone.
- Purification: Disrupt cell membranes, denature proteins, separate DNA.
- Quantification: Assess DNA amount for testing.
Amplification:
- Required DNA amount for testing is between 0.5-2.5 nanograms, amplified using Polymerase Chain Reaction (PCR).
- PCR creates 100 million to 1 billion copies of targeted DNA.
Electrophoresis:
- Analyzes DNA profiles based on electrical charge and mass, producing an electropherogram (EPG).
- Comparing unknown DNA profiles to known profiles, typically requires matching at 10 loci.
Statistical Analysis of DNA:
- Probability of identical DNA sequences decreases as more loci are compared (e.g., Ace of Cards analogy).
- Fewer matches indicate unique DNA profiles; 10 loci match is rare in populations.

Purpose:
- Replaced outdated methods of forensic sample collection with updated regulations.
- Established a DNA database for criminal investigations and for helping locate missing individuals.
- Regulates samples taken from both suspects and volunteers.
Advantages:
- DNA analysis quickly excludes or includes individuals in investigations.
- Assists in exonerating wrongful convictions, but not infallible.
Concerns:
- Technical risks and potential violation of fundamental rights (Council of Europe Recommendation, 1992).

Incident Overview:
- Armed robbery at Blackpool Post Office, March 26, 2009; about €20,000 stolen.
- Witness accounted for suspects’ actions, enabling evidence collection.
DNA Evidence:
- O’Callaghan’s DNA found on a balaclava linked to the robbery.
- Trial based on eyewitness testimony, his contradictory accounts, and DNA analysis.
Court Proceedings:
- O’Callaghan appealed conviction on grounds of insufficient evidence.
- Court found that the critical evidence was the DNA from the balaclava, but its interpretation was problematic.
Forensic Analysis of the Balaclava:
- Forensic scientist could create a DNA profile from samples taken from the balaclava.
- Major component matched O’Callaghan, but mix from other individuals led to ambiguity regarding who wore the balaclava.
Court Decision:
- Lengthy examination of the DNA evidence concluded insufficient basis to ascertain guilt.
- The Court ruled the trial outcome unsafe, leading to conviction being overturned based on unclear forensic evidence.