Key Takeaways:
- Forensic light sources are only intended to indicate the possible presence of biological fluids that require further testing.
- Identifying the biological fluid before testing has been undertaken is merely opinion and should never be included within a statement.
- Any forensic light source evidence presented in court without supporting supplementary testing can and should be dismissed.
Hollywood Has a Lot to Answer For
Hollywood has contributed to the widespread belief that forensic light sources used at crime scenes are infallible tools for identifying biological fluids. Unfortunately, this belief has taken hold even in modern courtrooms, where statements like the below are becoming more frequent:
“I conducted an examination of the underwear using forensic light sources. This examination indicated the positive presence of saliva in the crotch area.”
However, these lights can cause fluorescence of many things, including some forensically relevant biological fluids.
Forensic Light Sources Cannot Confirm the Presence of Any Biological Fluid
There are multiple types of forensic light sources that may be used at a crime scene. Each fluid reacts with different light sources in different ways.
All an investigator can ascertain with certainty from forensic light sources is the presence of a fluid. They cannot say with certainty which fluid it is.
Consider this image, which shows three fluid samples under forensic light: urine, semen, and saliva. A trained eye may be able to guess which is which, but this will be opinion, not evidence.
Non-Biological Materials Can Also Fluoresce
Non-biological materials, such as cleaning fluid, can also fluoresce. Positive results only indicate the need for further testing.
There is nothing about the detection of fluorescence or absorption of stains that can be used to reliably infer the type of biological material present.
These tools are just one of the first steps in the examination process, and there is very limited information that can be gleaned from the use of an alternate light source. It should be a guide for examiners for further testing.
Conclusion
Any statements including forensic light data must be supported by lab analysis, or they should be dismissed.
Do You Need an Expert Witness to Assist in Interpreting and Challenging Evidence?
Independent Forensic Services is led by Principal Forensic Scientist Jae Gerhard. With over 15 years of experience from crime scene to court, Jae offers unbiased, evidence-based, and easy-to-understand forensic opinion.
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Hear from One of Our Recent Clients
“I had the pleasure of working with Jae Gerhard from Independent Forensic Services on a complicated issue of DNA evidence in a criminal trial in Victoria in 2022. The trial involved an issue of interpreting the possible scenarios by which DNA was deposited on items of clothing, and Jae provided her reports in a good and timely way. Those reports were excellently researched as well as being very easy to understand. We spoke for a long time before Jae eventually gave sworn evidence at the trial, and she was able to describe to me in completely understandable language why it was that the conclusions that had been reached in the case by the police-funded Victorian Forensic Services Laboratory were able to be challenged. Jae then followed that up by giving evidence in the trial. She was an excellent and thoroughly knowledgeable witness who was able to describe things in a completely comprehensible way. The result of all of this was that the DNA evidence in the trial was excluded – as it should have been. So, I have no hesitation in recommending the expert services of Independent Forensic Services in general and of Jae Gerhard in particular wherever an issue to do with DNA evidence arises.”
C. Pearson, Barrister VicBar
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An Expert Team Lead by Jae Gerhard
Jae Gerhard is a Forensic DNA Expert and the Principal Forensic Scientist at Independent Forensic Services, bringing over two decades of frontline experience in forensic biology. She has worked on some of Australia’s most complex and high‑profile cases with the Australian Federal Police and New South Wales Police, as well as international disaster victim identification operations in Bali and Thailand.
Specialising in DNA analysis, STRmix™, biological fluid examination, and bloodstain pattern interpretation, Jae now works independently with criminal defence teams to review and challenge forensic evidence. Her mission is simple: to ensure the science presented in court is accurate, balanced, and truly understood.