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When is a ‘blood swab’ not a blood swab?
“The Blood Matches My Client”: A Common Assumption
What the Case Materials Actually Showed
1. Suspected blood at the crime scene
2. Presumptive Blood Testing Only
- – metals
- – cleaning agents
- – plant material
- – other biological fluids
3. No Confirmatory Blood Testing
4. No Visual Indication of Blood
5. Low-Level, Mixed DNA Profile
- – secondary transfer
- – environmental DNA
- – indirect contact
What Can – and Cannot – Be Scientifically Concluded
- – blood was present on the swab, or
- – any blood present belonged to the defendant.
- – a suspected bloodstain
- – a positive presumptive test with known limitations
- – a low-level mixed DNA profile including the defendant
How Forensic Assumptions Become Legal “Facts”
- A stain is suspected to be blood
- It is labelled a “blood swab”
- The label is repeated in reports
- Repetition creates shorthand
- Shorthand becomes assumption
- Assumption becomes accepted fact
Why This Matters for Criminal Defence Lawyers
- Was the substance scientifically confirmed to be blood?
- What specific tests were performed?
- What are the limitations of those tests?
- Does the DNA profile quality support strong conclusions?
- Are alternative explanations consistent with the findings?
A Perspective Shift in 15 Minutes
Conclusion: Always Question the Label
- What was actually tested?
- What was proven — and what was assumed?
