Biological Fluid Examination for Criminal Matters

Biological Fluid Examination

Biological fluids are materials produced by the human body, including blood, semen and saliva.

In forensic science, they matter because they can assist in determining what type of material was deposited, where it was deposited, and sometimes how it may have been deposited. When correctly identified, biological fluid findings can help a court evaluate propositions that go beyond identity — including whether the evidence is consistent with the alleged act itself.

That said, biological fluid evidence is frequently misunderstood. A stain described as “blood” or “saliva” can quickly become treated as fact, even when the material has only been suspected at the scene or supported only by limited screening results.

Robust scientific detection and classification of biological fluids is critically relevant in serious criminal matters. But biological fluids cannot, in and of themselves, be relied upon as to identity.

Rather, their forensic value often lies in what they may indicate about the nature of the material present, and whether that material is consistent with the alleged events.

 

Biological fluids are materials produced by the human body, including blood, semen and saliva.

In forensic science, they matter because they can assist in determining what type of material was deposited, where it was deposited, and sometimes how it may have been deposited. When correctly identified, biological fluid findings can help a court evaluate propositions that go beyond identity — including whether the evidence is consistent with the alleged act itself.

That said, biological fluid evidence is frequently misunderstood. A stain described as “blood” or “saliva” can quickly become treated as fact, even when the material has only been suspected at the scene or supported only by limited screening results.

Robust scientific detection and classification of biological fluids is critically relevant in serious criminal matters. But biological fluids cannot, in and of themselves, be relied upon as to identity.

Rather, their forensic value often lies in what they may indicate about the nature of the material present, and whether that material is consistent with the alleged events.

 

We assist criminal lawyers by:

  • – Reviewing reported biological fluid findings and associated forensic documentation
    – Evaluating the reliability and limitations of blood, saliva and semen testing
    – Identifying assumptions, interpretive gaps and alternative explanations
    – Preparing clear advice to support case strategy and decision-making
    – Delivering expert reports where required

 

  • Common issues seen in biological fluid reporting:
    – Presumptive testing reported as if confirmatory
    – False positives and non-specific reactions (substrate effects)
    – Limited sensitivity in low-level or aged stains
    – Blood” or “saliva” assumptions based on context or collection labels
    – DNA results being used to imply biological source without adequate support

Consider an independent review of the evidence when:

  • – The alleged biological fluid is pivotal to the prosecution or defence case
    – The result is based on presumptive testing (or confirmation is unclear)
    – The stain is limited, diluted, degraded, or very low-level
    – The findings are being used to imply source or activity (“it must be blood/saliva/semen”)

Depending on your needs we can provide:

  • Written advice / conference notes

  • Expert witness report

  • Cross-examination support materials

  • Case consultations via video conference

If you are unsure whether the forensic evidence warrants expert involvement, I can provide an initial view and a quote for the appropriate level of review — from targeted advice through to full reporting and trial support.

What we do

We assist criminal lawyers by:

  • – Reviewing reported biological fluid findings and associated forensic documentation
    – Evaluating the reliability and limitations of blood, saliva and semen testing
    – Identifying assumptions, interpretive gaps and alternative explanations
    – Preparing clear advice to support case strategy and decision-making
    – Delivering expert reports where required

 

Common issues
  • Common issues seen in biological fluid reporting:
    – Presumptive testing reported as if confirmatory
    – False positives and non-specific reactions (substrate effects)
    – Limited sensitivity in low-level or aged stains
    – Blood” or “saliva” assumptions based on context or collection labels
    – DNA results being used to imply biological source without adequate support
When to use us

Consider an independent review of the evidence when:

  • – The alleged biological fluid is pivotal to the prosecution or defence case
    – The result is based on presumptive testing (or confirmation is unclear)
    – The stain is limited, diluted, degraded, or very low-level
    – The findings are being used to imply source or activity (“it must be blood/saliva/semen”)
What you get

Depending on your needs we can provide:

  • Written advice / conference notes

  • Expert witness report

  • Cross-examination support materials

  • Case consultations via video conference
Quotation

If you are unsure whether the forensic evidence warrants expert involvement, I can provide an initial view and a quote for the appropriate level of review — from targeted advice through to full reporting and trial support.

DISCUSS BIOLOGICAL FLUID EVIDENCE IN YOUR CASE

Early, strategic advice is often informal and does not require a full report.

Why biological fluid identification matters in court

DNA is carried within biological material such as semen, saliva and blood — with semen and saliva most commonly relevant in sexual assault matters, and blood frequently central in assault cases and homicide investigations.

This means DNA may be deposited:

  • with a biological fluid (for example, semen or blood), or
  • without any identifiable biological fluid (for example, trace DNA / skin cells / contact DNA)

This distinction can be crucial.

Precise identification of the biological fluid type can provide a stronger evidential link between an individual and the alleged act itself, and in some matters it can be determinative as to the inculpatory or exculpatory value of the evidence.

The problem: biological fluids are often presumed, not confirmed

Laboratories frequently rely on screening (presumptive) tests that may suggest the presence of blood, semen or saliva, such as O-tolidine for blood or Acid Phosphatase (AP) as an initial semen screen. Presumptive testing is not inherently inappropriate — it is often a practical way to triage exhibits and guide further examination.

The problem arises when presumptive results are reported or relied upon as though they are definitive confirmation. Even tests sometimes described as “confirmatory”, including RSID and p30 (PSA) testing, have important limitations and must be interpreted cautiously in context.

In practice, further testing can reveal that no biological fluid is scientifically identifiable at all, despite the material being described as blood, semen or saliva within the report. This is not a minor detail. If the biological source has not been confirmed, the evidential interpretation can change substantially — and so can the issues that should be tested in court.

Helen Roebuck DNA expert witness sitting at a desk in front of lap top giving evidence

DNA without biological fluid: often a different proposition entirely

Cells containing DNA are highly transient.

The presence of a DNA profile in the absence of any identified biological fluid can be of significantly less evidentiary weight, depending on the circumstances.

This is because DNA may be detected following:

  • routine handling and contact
  • indirect transfer (secondary transfer)
  • background DNA
  • persistence effects
  • low-level deposition without biological fluid involvement

The forensic value often turns on whether the case involves a confirmed biological fluid, or whether the DNA finding is more consistent with trace DNA and the limitations of interpretation.

Semen evidence: What is proves (and what it doesn't)

In sexual assault matters, biological fluid findings can be case-defining. The detection of semen is often highly probative – but semen and DNA are not the same question.

Semen may be present without establishing whose semen it is, and a DNA profile may be reported without confirming the biological source. In some cases, the amount and distribution of semen detected can also be assessed against the allegation (including potential “time since” considerations).

Careful review is critical to ensure semen evidence is interpreted accurately — and not overstated in court.

 

In sexual assault matters, biological fluid findings can be case-defining. The detection of semen is often highly probative – but semen and DNA are not the same question.

Semen may be present without establishing whose semen it is, and a DNA profile may be reported without confirming the biological source. In some cases, the amount and distribution of semen detected can also be assessed against the allegation (including potential “time since” considerations).

Careful review is critical to ensure semen evidence is interpreted accurately — and not overstated in court.

 

False Positive

Biological fluid false positives regularly occur with the use of presumptive testing.
Presumptive testing is the common method used by Australian laboratories and relied upon in the subsequent report.
Caution is advised to avoid any assumption that a presumptive test is conclusive.
Presumptive biological tests are convenient and low cost.
They can yield a false positive to other biological and non-biological matter such as vaginal fluid, faecal matter, blood, rust and bleach.
Interpreting biological fluid test results requires careful consideration by a skilled forensic scientist, to avoid any mis representation before the court.

Error Rate

The error rate in biological fluids evidence before the courts, spans two areas, which are interconnected.
Firstly, presumptive testing, is regularly relied upon to confirm biological fluids, when it should more appropriately be confirmatory testing that is relied upon.
Secondly and subsequently, the presumptive positive is relied upon to infer that the biological fluid (apparently identified) is connected to the individual by virtue of the entirely separate DNA likelihood ratio.
The relationship between given biological fluids and the DNA are regularly of critical significance in a matter. and require careful and highly skilled consideration.

Contamination

Biological fluid contamination can occur during medical examination, crime scene investigation and within the laboratory.
Appropriate anticontamination protocols should be strictly maintained.
Subtle means of body fluid contamination can occur between locations (transfer) of a particular item of interest. This can be of specific importance when the exacting location of the said body fluid is relevant to the confirmation or refutation of the alleged facts.
Contemporaneous notes from biological fluid examinations along with the DNA results, can adduce further information as to the likelihood and potential implication of contamination.

Bodyfluid Testing

Presumptive testing of biological fluids such as blood, semen and saliva are commonplace, and known to produce false positives.
Confirmatory testing should be conducted when the type or true existence of body fluid is critical to the facts of an alleged crime.
Accurate testing and interpretation of biological fluids as to the individual and type can contribute substantially to a matter.
The critical importance of body fluids testing is understood, when the erred testing of fluids negates the courts weighting of a robust DNA match within a matter.
Roebuck Forensics can conduct confirmatory testing on suspected biological fluids.

Crime scene examination

DNA and biological fluids are very commonly sampled together and subsequently inferred, and perhaps assumed to be a singular deposition.
Conjunctive evaluation of DNA and biological fluids as sampled, is not in all circumstances scientifically well founded.
DNA is regularly reported with the apparent inference, that it originates from the body fluid sample, when confirmatory testing reveals that no such inference is supportable.
The highly transient nature of both DNA and biological fluids dictates that very careful consideration should be applied to their combined relationship within the crime scene evidence.

Time since event

Time since event can be of critical relevance in sexual assault matters, as to the question of semen deposition.
Caution is advised when relying upon subjective testing of fluids.
A common scenario is one where ejaculation is alleged, though semen cannot be scientifically identified with confirmatory testing.
Internally deposited semen rapidly degrades in quantity and structure due to biological and environmental factors, with the likelihood of a true positive fading rapidly in the time since intercourse (TSI).
Deposited fluids can degrade rapidly over time due to environmental factors, with published data being useful in limited scenarios.
False positive

False Positive

Biological fluid false positives regularly occur with the use of presumptive testing.
Presumptive testing is the common method used by Australian laboratories and relied upon in the subsequent report.
Caution is advised to avoid any assumption that a presumptive test is conclusive.
Presumptive biological tests are convenient and low cost.
They can yield a false positive to other biological and non-biological matter such as vaginal fluid, faecal matter, blood, rust and bleach.
Interpreting biological fluid test results requires careful consideration by a skilled forensic scientist, to avoid any mis representation before the court.
Error rate

Error Rate

The error rate in biological fluids evidence before the courts, spans two areas, which are interconnected.
Firstly, presumptive testing, is regularly relied upon to confirm biological fluids, when it should more appropriately be confirmatory testing that is relied upon.
Secondly and subsequently, the presumptive positive is relied upon to infer that the biological fluid (apparently identified) is connected to the individual by virtue of the entirely separate DNA likelihood ratio.
The relationship between given biological fluids and the DNA are regularly of critical significance in a matter. and require careful and highly skilled consideration.
Contamination

Contamination

Biological fluid contamination can occur during medical examination, crime scene investigation and within the laboratory.
Appropriate anticontamination protocols should be strictly maintained.
Subtle means of body fluid contamination can occur between locations (transfer) of a particular item of interest. This can be of specific importance when the exacting location of the said body fluid is relevant to the confirmation or refutation of the alleged facts.
Contemporaneous notes from biological fluid examinations along with the DNA results, can adduce further information as to the likelihood and potential implication of contamination.
Testing

Bodyfluid Testing

Presumptive testing of biological fluids such as blood, semen and saliva are commonplace, and known to produce false positives.
Confirmatory testing should be conducted when the type or true existence of body fluid is critical to the facts of an alleged crime.
Accurate testing and interpretation of biological fluids as to the individual and type can contribute substantially to a matter.
The critical importance of body fluids testing is understood, when the erred testing of fluids negates the courts weighting of a robust DNA match within a matter.
Roebuck Forensics can conduct confirmatory testing on suspected biological fluids.
Crime scene

Crime scene examination

DNA and biological fluids are very commonly sampled together and subsequently inferred, and perhaps assumed to be a singular deposition.
Conjunctive evaluation of DNA and biological fluids as sampled, is not in all circumstances scientifically well founded.
DNA is regularly reported with the apparent inference, that it originates from the body fluid sample, when confirmatory testing reveals that no such inference is supportable.
The highly transient nature of both DNA and biological fluids dictates that very careful consideration should be applied to their combined relationship within the crime scene evidence.
Time since event

Time since event

Time since event can be of critical relevance in sexual assault matters, as to the question of semen deposition.
Caution is advised when relying upon subjective testing of fluids.
A common scenario is one where ejaculation is alleged, though semen cannot be scientifically identified with confirmatory testing.
Internally deposited semen rapidly degrades in quantity and structure due to biological and environmental factors, with the likelihood of a true positive fading rapidly in the time since intercourse (TSI).
Deposited fluids can degrade rapidly over time due to environmental factors, with published data being useful in limited scenarios.
Helen Roebuck DNA expert Sydney

Why Roebuck Forensics

I have worked across every part of the forensic process - from crime scenes, to laboratory interpretation, to expert witness testimony.

My focus is not simply the presence of DNA or a statistic.

It is what the evidence can actually support — in the context of the case.

Next Step

If you’d like to discuss whether the forensic evidence in your matter warrants further review:

Contact Roebuck Forensics

A preliminary review can be a useful step in assessing the broad strengths and weaknesses of a particular matter. This process can also identify documentary and any further evidence requirements.

I rigorous interrogation of the evidence will uncover underlying issues and determine the most appropriate pathway towards reviewing and reporting the matter.

Certain complex matters benefit from a draft report, which can open areas for discussion with Counsel, and potentially allow for defence to approach the prosecution.

Following a thorough evaluation of the evidence, a DNA expert report will be issued in accordance with the expert witness code of conduct. The report will be suitable for submission in evidence.

Preparations with Counsel are often conducted, such that the probative value of the evidence is weighed effectively and persuasively at Voir Dire, should such a hearing be required.

Extensive preparations are generally conducted in anticipation of substantive hearing. Which may include cross examination and evidence in chief scenarios specific to the matter .

Biological Fluids QUESTIONS

What are biological fluids in forensic science?

Biological fluids relevant to forensic science include blood, urine, faeces, vomit, semen, sweat, saliva and bodily secretions.

Blood

Blood is often shed during violent crimes, and can be DNA tested to determine the donor.  Blood also lends itself to the science of Bloodstain Pattern Analysis which can be conducted to determine the sequence of events or actions that may have created the bloodstains.

Semen

Semen can be recovered from within the vagina for several days after sexual intercourse.  A DNA profile can be obtained from semen, even when it does not contain sperm cells (ie the male is vasectomised).

Saliva

Saliva may be relevant to the investigation of many crimes.  Whilst it is more difficult to identify than other biological fluids, a DNA profile can be obtained allowing identification of the source.

Likelihood Ratio

The likelihood ratio presented in DNA reports typically addresses the identity of the individual only and not the biological fluid origin.

Activity level reporting

Activity level reporting seeks to consider the ‘how’ rather than the ‘who’

Body fluid method of deposition

In some cases it is possible to consider how the fluid was deposited.  For example, in bloodstain pattern analysis.

Time since intercourse

Semen rapidly deteriorates within the body.  The amount of semen detected within the vagina can be assessed to determine when intercourse occured.

Transfer of bodily fluids around a single item

Biological fluids can be transferred from one part of an item to another.  THis occurs more frequently when the fluid is wet, however dry fluids may also be transferred.

Transfer within exhibit packaging

Studies have demonstrated that biological fluids can be redistributed within exhibit packaging.

Sexual assault

Vaginal fluids identification

There is currently no test available for robust identification of vaginal fluids.

Semen survival within the vagina

Semen can remain in the vagina for several days, depending on factors such as washing/douching, menstruation and physical activity.

DNA without ejaculation

The amount of DNA deposited is far lower than if ejaculation occurred.  As such, specialist DNA testing known as Y-STR testing is often required.

Biological fluid reporting

Negative biological fluid reporting

“No blood was observed” should not be taken to mean that testing for blood was conducted.  It may well simply mean that the examiner did not readily observe blood with the naked eye.

Biological fluid false positive

The majority of body fluid testing results within a report are the result of presumptive testing.  Presumptive tests cannot be relied upon conclusively as they are known to provide positive results wiht other substances.  For example, the presumptive test for semen can also produce a ‘false positive’ result with vaginal material.

Identifying a person using biological fluids

Biological fluids contain DNA; however the success rates will vary dependent on several factors, including the amount of biological fluid present.

Facts

Average semen volume

3-5ml (or a tea spoon).  Not all semen contains spermatozoa, with factors such as age, drug use and vasectomy affecting sperm count.

Vasectomised males and semen

Semen produced by a vasectomised male contains very low numbers of, or no, sperm cells.  However, it is still possible to detected semen from a vasectomised male and to obtain a DNA profile from cells other than sperm cells, deposited during sexual intercourse.

Blood grouping and forensic science

DNA profiling has supersded the use of blood grouping in forensic science.  Fore example, roughly 30% of the population has type-A positive blood.  Therefore, if A-positive blood were found at the crime scene, it could have come from approximately 30% of the population.  DNA profiling has a much greater discriminating power.

Use of UV light

Alternate light sources using varying wavelengths of light such as Ultra Violet, are often portrayed on television as a key crime scene examination tool.  Whilst they can be a valuable tool for locating biological fluids, they only indicate the possible presence of a substance.  Fluorescence can be emitted under alternate wavelength lighting from many substances, including cleaning products.

Court

Dialogue with the Crown expert

Differing jurisdictions participate in dialogue within varying degrees of formality.  Our recommendation is that we steer the technical aspects of any approach.

Reports in reply

Our reports regularly bring about concessions which may be delivered by way of a report in reply, or in certain circumstances, a withdrawal of evidence.

Presumptive testing

Presumptive testing may lead to the request for confirmatory testing, though counsel may well apply a strategic consideration to the matter.

Laboratory testing

Decision to use confirmatory testing

Presumptive biological fluid testing is largely an investigative tool, giving an indication as to whether confirmatory testing is likely to bare fruit.  Certain labs readily apply confirmatory testing, and others conduct confirmatory testing very sparingly.

Spermatozoa and semen

Detection of spermatozoa cells (sperm cells) may not mean there is a deposit of ejaculate.  Sperm cells can be readily distributed through laundering.

UV light (alternate light source)

UV light is regularly utilised within the lab to locate biological fluids.  This is an investigative tool and does not at all mean that a confirmatory test for biological fluids has been conducted.

Terms

Presumptive test

Presumptive, or screening, tests make use of a target chemical to establish the possibility that a specific body tissue or fluid is present. Presumptive tests are known to also react to other substances.

 

Confirmatory test

A confirmatory test is one which is specific to the body fluid in question and does not obtain false positives with other substances.

Orthotolidine Test

The orthotolidine test, also known as O-tol , is a presumptive chemical test used for the detection of possible blood.  In the presence of blood, O-tol undergoes a colour change reaction.  O-tol also reacts to substances including rust and bleach.

Hemastix

Hemastix are test strips used for the detection of possible blood.  They are often used by crime scene examiners due to their ease of use and portability.  Hemastix are a presumptive test only and also react to other substances such as vegetable matter and rust.

RSID

Rapid Stain Identification (RSID) refers to a specific type of immunochromatographic tests, which are in the form of test strips similar in appearance to a pregnancy test. These tests are available for blood, semen, saliva and urine testing.

RSID Semen

The RSID semen test is a confirmatory test for the presence of semen.

 

p30 test

p30 is a a test for the prostate specific antigen found in semen.  Once considered a confirmatory test for semen, research has show that this test can cross react with other biological fluids such as urine and breast milk.

 

Acid phosphatase

Acid phosphatase is an enzyme found at high levels in semen.  Acid phosphatase testing involves the application of a chemical reagent to detect acid phosphatase.  It is a useful screening tool for locating possible areas of semen staining, however it can also react with other substances, including vaginal material.

Hematrace

Hematrace is a confirmatory test for the presence of blood.  It will produce a positive results with human, some primates and ferret blood.

Phadebas

Phadebas is a presumptive test for the presence of saliva.  It detects the enzyme amylase which is present in other biological fluids such as sweat and vaginal material.

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