- handling at the crime scene
- packaging and transport
- laboratory processes
- indirect transfer between people and surfaces

DNA Contamination in Criminal Cases: WA v Piccioni Explained

1. The allegation

It was alleged that firearms within a locked shed belonged to the defendant.
DNA testing by the state laboratory identified a DNA profile matching the defendant.
The DNA results upon firearms were substantially relied upon to support the prosecution.

2. THE BACKGROUND

Sexual assault – DNA excluded pre-trial →

3. What the DNA report did and didn’t say

The lab report identified DNA matching the accused.
The report did not identify DNA matching the other person who accessed and had goods within the shed.
Almost always, the DNA report will not review or report the sampling or crime scene handling.
In this case, there had been issues raised by the defence to the prosecution about the crime scene handling, and the lab expert had reviewed and subsequently reported upon the search footage.
The report set out a series of issues with the police handling of items.
The report went on to state – “Whilst the above outlines flaws in the contamination minimisation techniques employed in this instance, there is no expectation that DNA transfer (contamination) has occurred as a result of such flaws.”

4. The Pre-Trial Contamination Hearing

The admissibility of the DNA evidence was challenged by defence.
Courts assess admissibility of DNA evidence using established evidentiary principles.
An early hearing (voir dire) was held, where the parts of law and science were put before the judge.
The experts in this case were not cross examined, and the judge gave consideration to the reports of both experts.
The lawyers made detailed submissions to the judge.
The judge described the courts task: My role in determining this application is to determine whether the prejudicial effect of the proposed DNA evidence outweighs any probative value it might hold.

5. Why the DNA evidence was refused

The issue in this case was not whether DNA was detected.
The question became, could this DNA evidence support the allegation, and should a jury hear it?
That question is part legal and part scientific.

6. How DNA Evidence Can Be Challenged in Court

Contemporaneous notes and witness statements
Substantial video footage
Electropherograms
DNA statistics
Published scientific research data
The two substantive reports

7. How DNA contamination applies to your matter

Any DNA profile may be the result of or suffer from contamination.
Contamination may occur at the crime scene, during packaging, during transport, or within the laboratory environment.
The mere possibility would generally not be sufficient to warrant challenge.
Proper consideration of DNA contamination requires a scientific review.
A particular allegation requires careful scientific evaluation of the pathways by which DNA may have been deposited.

- interrogation of the DNA casefile
- review of electropherograms
- assessment of number of contributors
- review of contamination records
- consideration of sampling notes
- evaluation of item handling and seizure procedures

1 billion DNA statistic – challenged – withdrawn →

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