CAN DNA EVIDENCE BE CONTAMINATED ?
Yes - DNA evidence can be contaminated
DNA contamination is the introduction of unrelated DNA into a sample during collection, handling, or laboratory analysis.
Contamination can leave a DNA profile when that person was never involved in the allegation.
Contamination is a regular occurrence with DNA evidence.
Contaminated DNA does not look different.
Contaminated evidence cannot be evaluated from the lab report.
Modern DNA testing is highly sensitive, meaning even very small traces of DNA can be detected.
The presence of DNA does not reveal how or when the DNA got there.
It is critical to establish the contamination pathway when contamination is suspected.
Contaminated DNA evidence may be unreliable or ruled inadmissible.
DNA contamination
DNA contamination can occur during evidence collection, handling, or laboratory testing.
During evidence collection, contamination may arise from contact between items, inadequate handling procedures, or transfer from personnel involved in the examination. Packaging and storage can also introduce opportunities for DNA to move between exhibits.
Within the laboratory, contamination risks are managed, however the potential for introduction or transfer of DNA remains.
Highly sensitive testing methods mean that even trace amounts of DNA may be detected.
Contamination is not limited to a single action and may involve multiple events across the lifecycle of the evidence.
DNA contamination can affect the interpretation of results by introducing DNA that is unrelated to the allegation.
This may result in a DNA profile being reported that appears relevant, when in fact it is not.
In mixed DNA profiles, contamination may contribute additional alleles, complicating interpretation and potentially influencing statistical calculations.
The presence of DNA alone does not distinguish between genuine deposition and contamination.
DNA results may be overstated if contamination is not properly considered.
Contaminated DNA looks no different from uncontaminated DNA in the lab report.
A contamination review involves thorough scientific review of the entire lifecycle of all samples from collection, to sampling and within the laboratory.
Video footage is increasingly common in the review of crime scene collection and handling.
Witness statements can provide useful picture of handling items prior to seizure.
Chain of custody consideration is routine.
A thorough review of the Forensic laboratories controls and safeguards, such as negative controls, batch processing checks, and staff elimination databases may be necessary.
DNA evidence in Australia is generally admitted by the court, unless challenged by defence.
The value of DNA is limited when contamination is identified or shown to be viable.
In some circumstances, contamination issues may lead to DNA evidence being excluded entirely, particularly where the reliability of the result cannot be established.
The thorough scientific evaluation of potential contamination is therefore central to understandingwhether the DNA can be relied upon at all.
