Can DNA evidence be wrong?
Yes - DNA evidence can be wrong
DNA evidence can be wrong, overstated, or misinterpreted — even where it appears strong.
Errors can arise from contamination, transfer, mixed DNA profiles, sampling choices, and how results are interpreted and reported.
DNA can transfer between people, objects, and environments — meaning your DNA may be present even where you have never touched the item.
DNA identifies biological material — it does not explain how it was deposited, when it was left, or what activity led to its presence.
A DNA “match” does not mean the DNA was deposited during the alleged events.
When DNA evidence is wrong
DNA evidence can be wrong due to contamination, lab error, or imprecise reporting.
DNA transfer — DNA can move between people, objects, and environments without direct contact.
Contamination — DNA may be introduced during crime scene handling, packaging, or laboratory processes.
Mixed DNA profiles — interpretation depends on assumptions about contributors and mixture composition.
Reporting — statistical results can be misunderstood, overstated, or applied to questions they do not answer.
Determining whether DNA evidence is reliable requires examination beyond the expert report issued by the state laboratory.
The report presents selected results — it does not set out the full testing process, nor assess whether those results scientifically support the alleged activities.
A proper review involves examination of the underlying DNA casefile material.
Review may include:
Electropherograms — assessment of peak heights, imbalance, degradation, and artefacts
STRmix or probabilistic genotyping outputs — including assumptions about contributor number and model settings
Number of contributors — whether this has been correctly assigned or constrained
Population database selection — whether the reported statistic reflects the relevant population
Alternative propositions — whether competing explanations have been properly evaluated
Laboratory documentation — including contamination records, handling notes, and sampling pathways
These factors can materially affect the strength — and meaning — of the DNA evidence.
The reliability of DNA evidence depends on the circumstances of the particular case, not just the presence of DNA alone.
It depends on what was tested, how the items were handled, where the DNA was found, and whether the results actually support the allegation — or a different explanation.
