bloodstain pattern analysis

Blood can be powerful evidence.

But bloodstain pattern evidence is often treated as if it can prove what happened.

Bloodstain pattern analysis (BPA) is the forensic examination of bloodstains to assist in interpreting how blood was deposited. It draws on principles of physics (alongside biology and careful crime scene evaluation) to assess bloodstain size, shape, distribution and directionality, and to evaluate issues such as mechanism, movement, and whether competing accounts are consistent with the physical evidence.

Roebuck Forensics provides independent bloodstain pattern analysis review for criminal lawyers across Australia and New Zealand, including matters where BPA evidence is central to the prosecution case or defence case strategy.

Blood can be powerful evidence.

But bloodstain pattern evidence is often treated as if it can prove what happened.

We can provide:
– Review of bloodstain pattern analysis reports
– Assessment of bloodstain evidence in scene photos
– Evaluation of terms such as impact spatter and cast off
-Identification of alternative explanations and limitations
– Laboratory examination of clothing and weapons

Issues we frequently observe in BPA evidence:
– Conclusions that go beyond what the stains can reliably support
– Mechanism opinions offered without adequate scene context or testing
– “Cast-off”, “impact”, or “arterial” labels applied too definitively
– Limited scene documentation (photography, measurements, scale, continuity)
– Alternative explanations not properly considered
– Overstatement of certainty in reports intended for court

Contact us when:
– Blood evidence is pivotal to the prosecution or defence narrative
– The conclusion appears stronger than the scene documentation supports
– The Crown case relies on BPA to infer sequence, movement, or intent
– There are alternative explanations that have not been properly tested
– The scene is complex, dynamic, or has signs of disturbance or cleanup

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 can provide:
– Review of bloodstain pattern analysis reports
– Assessment of bloodstain evidence in scene photos
– Evaluation of terms such as impact spatter and cast off
-Identification of alternative explanations and limitations
– Laboratory examination of clothing and weapons

Common issues

Issues we frequently observe in BPA evidence:
– Conclusions that go beyond what the stains can reliably support
– Mechanism opinions offered without adequate scene context or testing
– “Cast-off”, “impact”, or “arterial” labels applied too definitively
– Limited scene documentation (photography, measurements, scale, continuity)
– Alternative explanations not properly considered
– Overstatement of certainty in reports intended for court

When to use us

Contact us when:
– Blood evidence is pivotal to the prosecution or defence narrative
– The conclusion appears stronger than the scene documentation supports
– The Crown case relies on BPA to infer sequence, movement, or intent
– There are alternative explanations that have not been properly tested
– The scene is complex, dynamic, or has signs of disturbance or cleanup

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

DISCUSS BLOODSTAIN EVIDENCE IN YOUR CASE

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

What is bloodstain pattern analysis?

Bloodstain pattern analysis (BPA) involves the assessment of bloodstains to consider factors such as:

blood origin and distribution
directionality and bloodletting dynamics
potential positions of persons within the scene
movement through the scene after bleeding began
whether an account is consistent with the physical evidence
whether there is evidence of disturbance, transfer, or staging

Unlike identification evidence, BPA is not about “whose blood is it?” It is about what the bloodstain pattern may indicate about what occurred, and what alternative explanations remain viable.

Key bloodstain pattern terms

Bloodstain pattern analysis frequently involves terminology that sounds definitive. In practice, these terms describe features, not conclusions.

Impact spatter describes bloodstains created when force is applied to a blood source, causing droplets to disperse.

Impact spatter may occur during assaults, but interpretation must consider:

the nature of the blood source and surface
the environment and disturbance
whether transfer or movement may explain similar staining
the limitations of available documentation (photography, scale, context)

Cast-off describes blood being flung from a moving blood-bearing object.

Cast-off patterns can sometimes assist in considering repeated motion, but they are not always present, and their interpretation can be context dependent.

Transfer stains occur when a bloodied surface contacts another surface.

Smears and wipes may occur where wet blood is disturbed. These patterns can be highly relevant in cases involving movement, contact events, or scene alteration.

Passive stains occur under gravity alone.

Passive bloodstain patterns can assist in evaluating whether an injured person was stationary or moving, whether bleeding continued in one location, and whether the distribution of stains fits competing accounts.

Case example: when “impact spatter” becomes the wrong shortcut

Consider a scenario of a kind that arises frequently in practice.

A complainant is found injured inside a residence.

The allegation is that the assault occurred in one room during a confrontation.

Crime scene photographs show scattered small bloodstains on a nearby wall.

The police report may describe the blood staining as “impact spatter”, and the room may then be treated as the confirmed assault location.

But an independent bloodstain pattern analysis review may require further questions to be addressed, including:

Are the wall stains actually consistent with impact, or could they be explained by passive dripping combined with movement?

The analysis may not provide a single definitive answer – but it can clarify what the blood evidence genuinely supports, and where assumptions have been made.

Consider a scenario of a kind that arises frequently in practice.

A complainant is found injured inside a residence.

The allegation is that the assault occurred in one room during a confrontation.

Crime scene photographs show scattered small bloodstains on a nearby wall.

The police report may describe the blood staining as “impact spatter”, and the room may then be treated as the confirmed assault location.

But an independent bloodstain pattern analysis review may require further questions to be addressed, including:

Are the wall stains actually consistent with impact, or could they be explained by passive dripping combined with movement?

The analysis may not provide a single definitive answer – but it can clarify what the blood evidence genuinely supports, and where assumptions have been made.

BPA Error rate

The error rate of bloodstain pattern analysis and the reliability of bloodstain expert evidence has been the subject of significant scientific and jurisdictional attention. The National Academy of Sciences released a report in 2009 stating that conclusions were often “more subjective than scientific” and open to “context bias”.

Further, a study of 75 BPA analysts in 2021 found that 11% erroneously identified bloodstain pattern (classification) types.

Our experience is that bloodstain pattern analysis can be highly useful in certain circumstances, though great care and skill must be applied to the evidence.

Conclusivity

The reliability and conclusively of bloodstain pattern analysis strongly rests within the extent and nature of propositions that one is seeking to consider.

Bloodstain pattern analysis is largely a subjective field, with the analyst seeking to answer questions about the manner and sequence of events, through the resultant bloodstains.

The analyst must exercise great caution and discretion when setting parameters as to what the evidence is fundamentally capable of supporting.

For example, transfer stains have been erroneously reported as impact spatter, having catastrophic outcomes for the justice system.

Evidence Tampering

Crime scene evidence tampering is frequently encountered when inspecting bloodstain pattern evidence.

Rudimentary weapon and hand wipe down, can extend through to sophisticated efforts to chemically remove bloodstain and DNA evidence.

Clean up attempts can drastically alter the bloodstain patterns, risking erroneous interpretation. An experienced analyst should identify clean-up efforts through interpretation of altered bloodstains such as wipes and swipes, and the presence of voids in patterns.

Bloodstaining and DNA are readily removed during laundering, however residual deposits are frequently trapped in areas such as stitching and zippers.

Luminol

Luminol is a chemical used in forensic investigation, which emits light (luminesce) upon contact with blood. It is highly useful to detect blood that cannot be visually observed, and where crime scene clean-up is suspected.

Luminol has a known propensity to react with some cleaning products including bleach.

Where luminol reactions are observed, confirmation of blood should be obtained through confirmatory testing. The observation and recovery of obscured and concealed blood, may require extensive physical searching of crevices. and would subsequently be utilised to conduct DNA testing for consideration of identity.

BPA Contamination

Contamination or crime scene alteration occurs frequently, through offender efforts to clean up, or unintended acts.

Homicides and serious assaults often involve first responders such as paramedics and police officers seeking to preserve life, which invariably result in alteration or production of new bloodstain patterns, for example through CPR attempts.

Insect activity can occur, with flies feeding on blood and regurgitating it to new locations, with this ‘fly speck’ testing positive for blood and having the appearance of blood spatter.

Skilled and realistic assessment of the crime scene can help establish events.

Crime scene examination

Accurate crime scene examination is crucial to bloodstain pattern analysis.

Meticulous recording of the bloodstain patterns through extensive photography and note taking is required for thorough evaluation and review of bloodstain patterns.

BPA often invokes the assumption that all reddish/brown visible staining is the consequence of the bloodshed event in question. A robust assumption in this regard can only be evidenced once sufficient testing of the staining has established that the stain is in fact blood.

Bloodstain review is commonly conducted upon high resolution photographs.

We can advise and conduct a physical crime scene examination should it be required.

Error rate

BPA Error rate

Further, a study of 75 BPA analysts in 2021 found that 11% erroneously identified bloodstain pattern (classification) types.

Our experience is that bloodstain pattern analysis can be highly useful in certain circumstances, though great care and skill must be applied to the evidence.

Conclusivity

The reliability and conclusively of bloodstain pattern analysis strongly rests within the extent and nature of propositions that one is seeking to consider.

Bloodstain pattern analysis is largely a subjective field, with the analyst seeking to answer questions about the manner and sequence of events, through the resultant bloodstains.

The analyst must exercise great caution and discretion when setting parameters as to what the evidence is fundamentally capable of supporting.

For example, transfer stains have been erroneously reported as impact spatter, having catastrophic outcomes for the justice system.

Tampering

Evidence Tampering

Crime scene evidence tampering is frequently encountered when inspecting bloodstain pattern evidence.

Rudimentary weapon and hand wipe down, can extend through to sophisticated efforts to chemically remove bloodstain and DNA evidence.

Bloodstaining and DNA are readily removed during laundering, however residual deposits are frequently trapped in areas such as stitching and zippers.

Luminol

Luminol has a known propensity to react with some cleaning products including bleach.

Contamination

BPA Contamination

Contamination or crime scene alteration occurs frequently, through offender efforts to clean up, or unintended acts.

Insect activity can occur, with flies feeding on blood and regurgitating it to new locations, with this ‘fly speck’ testing positive for blood and having the appearance of blood spatter.

Skilled and realistic assessment of the crime scene can help establish events.

CRIME SCENE

Crime scene examination

Accurate crime scene examination is crucial to bloodstain pattern analysis.

Meticulous recording of the bloodstain patterns through extensive photography and note taking is required for thorough evaluation and review of bloodstain patterns.

Bloodstain review is commonly conducted upon high resolution photographs.

We can advise and conduct a physical crime scene examination should it be required.

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 .

Professional Memberships

University of Technology Sydney – Industry Fellow

Helen Roebuck is honoured as an Industry Fellow at the University of Technology Sydney since 2012.

This recognition, draws upon current and past experience as an operational forensic scientist and expert witness. Crucial knowledge passes from the judicial system back into academia, whilst continued scientific developments filter into the courts.

This symbiotic exchange fosters continued learning and development between the inherently different, yet intrinsically intertwined strains of practice. Far from stagnant, forensic science is a continuum of development, which purposefully seeks to contribute meaningfully to the justice system.

Australia and New Zealand Forensic Science Society

The AFS (Australian Forensic Society) was formed in 1971 to bring together scientists, police, criminalists, pathologists, and legal professionals actively involved in the field of forensic science. In 1988, the AFS recognised New Zealand members and changed its name to ANZFSS.

The main objective is to enhance quality and advance expertise in the field of forensic science. ANZFSS members, are bound by a code of practice, which intends to provide a clear and concise summary of the professional roles and responsibilities of forensic practitioners. Practitioners also have responsibilities to the justice system.

Australian Academy of Forensic Sciences

The Australian Academy of Forensic Sciences brings together persons of professional standing from the legal, medical and scientific professions whom have contributed to the advancement or practice of forensic science. Founded in 1967 by Oscar Schmalzbach, the AAFS, is a learned body dedicated to the advancement of the forensic sciences, which allows membership by invitation. The Academy’s formal aims and objectives include to improve the practice and advance the knowledge of forensic sciences, and widen, improve and develop the education and knowledge both of those actively concerned in the pursuits of the forensic sciences and of the public.

Chartered Society of Forensic Sciences

The Forensic Science Society was founded in 1959. Now accepting memberships globally the CSOFS is the peak professional body for forensic practitioners, academics, researchers and associated professions in the United Kingdom.

In 2014, the Society was granted a Royal Charter and became The Chartered Society of Forensic Sciences.

The CSOFS is recognised as the ‘international voice of forensic science’.

The Chartered body is committed to integrity and impartiality, aiming to provide opportunities for practitioners and academics to congregate, communicate and collaborate.

The Society is committed to integrity and impartiality.

Bloodstain pattern analysis

Bloodstain pattern analysis uses the physical properties of blood, physics (including projectile motion and fluid dynamics) and mathematics (geometry, distance and angles) to interpret bloodstains and recreate the actions that caused them.

Conducting BPA

Analysts assess the appearance, distribution, size, range, shape and spread of bloodstains to interpret the event.

Using photographs to conduct BPA

High resolution photographs can be used to conduct BPA, but the photographs must be taken in a manner that facilities interpretation.

Error rate

A study in 2023 demonstrated that on average BPA analysts incorrectly categorised bloodstains 11% of the time.

Bloodstain pattern analysis - terms

Bloodstain

A deposit of blood on a surface.

Bloodstain pattern

A grouping or distribution of bloodstains that indicates through regular or repetitive form, order, or arrangement the manner in which the pattern was deposited.

Altered stain

A bloodstain with characteristics that indicate a physical change has occurred.

Angle of impact

The acute angle (alpha), relative to the plane of a target, at which a blood drop strikes the target.

Area of origin

The space in three dimensions to which the trajectories of spatter can be utilized to determine the position of the spatter producing event.

Backspatter pattern

A bloodstain pattern resulting from blood drops which can be produced when a projectile creates an entrance wound.

Cast off pattern

A bloodstain pattern resulting from blood drops released from an object due to its motion.

Cessation pattern

A bloodstain pattern resulting from blood drops released from an object due to its abrupt deceleration.

Directionality

The characteristic of a bloodstain that indicates the direction blood was moving at the time of deposition.

Drip pattern

A bloodstain pattern resulting from a liquid that dripped into another liquid, at least one of which was blood.

Drip stain

A bloodstain resulting from a falling drop that formed due to gravity.

Drip trail

A bloodstain pattern resulting from the movement of a source of drip stains between two points.

Expiration pattern

A bloodstain pattern resulting from blood forced by airflow out of the nose, mouth, or a wound.

Flow pattern

A bloodstain pattern resulting from the movement of a volume of blood on a surface due to gravity or movement of the target.

Forward spatter pattern

A bloodstain pattern resulting from blood drops which can be produced when a projectile creates an exit wound.

Impact pattern

A bloodstain pattern resulting from an object striking liquid blood.

Perimeter stain

An altered bloodstain which consists of its edge characteristics, the central area having been partially or entirely removed.

Pool

A bloodstain resulting from an accumulation of liquid blood on a surface.

Projected pattern

A bloodstain pattern resulting from the ejection of blood under hydraulic pressure, typically from a breach in the circulatory system.

Satellite stain

A smaller bloodstain that originated during the formation of the parent stain as a result of blood impacting a surface.

Saturation stain

A bloodstain resulting from the accumulation of liquid blood in an absorbent material.

Spatter stain

A bloodstain resulting from an airborne blood drop created when external force is applied to liquid blood.

Splash pattern

A bloodstain pattern created from a large volume of liquid blood falling onto a surface.

Swipe pattern

A bloodstain pattern resulting from the transfer of blood from a blood-bearing surface onto another surface, with characteristics that indicate relative motion between the two surfaces.

Transfer stain

A bloodstain resulting from contact between a blood-bearing surface and another surface.

Void

An absence of blood in an otherwise continuous bloodstain or bloodstain pattern.

Wipe pattern

An altered bloodstain pattern resulting from an object moving through a preexisting wet bloodstain.

Bloodstain Pattern Analysis Expert