Transcript Bloodstain Pattern Analysis (BPA)
Bloodstain Pattern Analysis (BPA)
Introduction to The Basics
Understanding the basics does not make one an expert!
Purpose of this lesson is to introduce you the topic of Bloodstain Pattern Analysis (BPA)
The take home lesson
archive bloodstain patterns because all bloodstain patterns contain important investigative information Archiving Sketching is not satisfactory for documenting bloodstain patterns except to show where they are and to record their breadth and width.
These are patterns Archive photographically & using video
Multitasking Evidence Provides investigators with a wide range of possible investigative information.
Whose blood is at the scene Distance from a target Direction of travel Energy of impact Handedness Relative position and movement of victim and assailant Minimum number blows Sequence of events and more
Historical Perspectives BPA in the United States
Blood leaves the human body or bloody covered object & produces interpretable patterns. Multiple scene types – Should expect to find at scenes of violent crimes and suicides. Interpreting what patterns reveal with respect to the events of the crime depends on reliability of experts … the training and experience.
WHO Analyzes Bloodstain Patterns
BPA has attracted individuals having diverse educational and professional backgrounds. Why? This seems shocking for a discipline supposedly having a basis in science. After all, shouldn’t science be practiced by scientists? The 2009 NAS report questions the scientific basis of pattern evidence, including BPA, because conclusions are seemingly based more on experience than scientific principle, even if the underlying basis of the conclusions is science-based.
Who Practices BPA?
Much of forensics is an amalgamation or partnership of forensic scientists and law enforcement professionals Crime scene investigation is largest sub discipline of forensics where science is practiced mostly by non-scientists and some scientists, each performing the same function.
Perform science at the scene,
Adopted BPA as investigative interest.
Crime laboratory scientists
Participate in the scene investigative scenario also adopted BPA as a sub specialty.
Non-scene forensic biologists
Crime Scene Investigators, Criminalists … Others Violent Crimes Bloodstain Patterns
BPA in the United States
Began arguably at the University of California Berkley with the work of Dr. Paul Kirk, a well known and respected forensic scientist. Kirk investigated the 1950’s murder of Dr. Sam Sheppard’s wife. Sheppard arrested and convicted of the crime but always claimed that an intruder entered his house and murdered his wife. Dr. Kirk went to the scene, wrote a brief for the court and testified concerning his belief that the bloodstain pattern evidence showed someone else was at the scene.
Kirk’s work in the case has become a legendary example of BPA. http://www.google.com/url?sa=i&source=images&cd=&cad=rja&docid=8dn8uff3UsupXM&tbnid=zWIiWIaC85mbIM:&ved= 0CAcQjB0wAA&url=http%3A%2F%2Fwww.corbisimages.com%2Fstock-photo%2Frights-managed%2FU1078663%2Fdr paul-kirk-criminologist-at-the sam&ei=mnVQUY3VFcri4AOQnYCgBA&psig=AFQjCNGSjsGDN0zNCc_LxtKciMGvqLDiqA&ust=1364313882405574
More Historical Perspectives
“Mockery of Justice” A book written by Sheppard’s son and Cynthia Cooper produced spotty DNA evidence suggesting Kirk’s interpretation was correct. Kirk’s work went largely unnoticed by police officials and crime scene investigators for whatever reason. Perhaps law enforcement didn’t like his interpretations OR thought it incorrect OR considered his work esoteric and beyond the skills of lay professionals, thus requiring a scientist of Kirk’s caliber.
Workshops for Law Enforcement
The next important work in this area was a booklet published by Herbert MacDonell, “
Flight Characteristics and Bloodstain Patterns of Human Blood
.” MacDonell’s experiments and research of other investigators throughout the world - caught the attention of law enforcement. Taking advantage of that interest, MacDonell began offering workshops designed to train law enforcement officers how to interpret bloodstain patterns. The result has been a proliferation of individuals working BPA cases throughout the United States. Most importantly, the simplicity of these workshops spawned a cadre of self-styled experts who also offered workshops and published books and articles.
Historical Overview – Cont.
MacDonell’s workshops and others that followed presented BPA in an easy-to-follow, lively and fun format, which was and continues to be offered in a not so rigorous a format, at least from an intellectual perspective. No written examinations or other traditional grading mechanisms, so no one feared failing the course. Everyone who attended and completed the course received a certificate of attendance, many of whom began practicing BPA in casework. PROBLEM: By requiring not much more other than completing a week-long course, attendees left with the feeling that BPA was simple enough for them to practice.
Recognizing the need for a formal organization around which the growing hoard of BPA analysts could communicate, MacDonell was instrumental in establishing the International Association of Bloodstain Pattern Analysts (IABPA). Now official journal.
Result of a proliferation of workshops On-going workshops and growing membership in the IABPA resulted in a proliferation of lay investigators, Many with dubious scientific and/or investigative credentials Performing BPA in casework working on both sides of the adversarial system. Ultimately their testimony has influenced the courts and thus has played a critical role in determining innocence or guilt.
The IAI split off BPA as a sub-discipline of crime scene investigation, considering it a separate discipline and began offering certifications. National Research Council’s NAS report of 2009 questions the scientific basis of BPA, practitioners dispute this. Forensic scientists in Minnesota in forefront of bloodstain pattern research and education reported in 2008 they believed BPA is a scientific endeavor. The following was taken from the introduction in their article:
“The blood patterns that form from such events often have recognizable characteristics that permit them to be classified into pattern types. It follows then that with a suitable understanding of these characteristics, investigators can draw certain inferences about the events and the mechanisms that led to the formation of the pattern. “However, a bloodletting incident is often a complex set of events which take place in three dimensional space. Blood volumes which are transferred generally undergo some change prior to their subsequent deposition on a surface. For example, a pool of blood is broken up into droplets of varying size which are projected outwards when the volume is subjected to an impact force. It is our contention that an understanding of the dynamics of these changes is critical to the sound interpretation of the resultant bloodstain pattern. “To date, investigators have mainly relied on observing many such patterns, coupled with laboratory simulation experiments, to build up experience in the recognition and classification of bloodstain patterns. Relatively little however, has been documented about
the dynamics of the blood transfer event
Labor and Epstein preempted the NAS report, warning other BPA analysts to move quickly to strengthen the discipline.
“… it is reasonable to assume that the courts will continue to demand the highest standards of forensic evidence and scrutinize with even more thoroughness each and every method behind the opinion of an expert witness. BPA is a discipline that has relied heavily on the experience of the witness. It is anticipated that a closer scrutiny
of the methods used in BPA will highlight the relative lack of underpinning scientific research and validation studies.
“It is critical therefore, that the BPA community moves quickly to strengthen the discipline with sound basic research to underpin the testimony of the analyst and give the courts the confidence they need in this testimony …”
Number of cases involving BPA increasing Standards needed: In 2002, the FBI began sponsoring a professional group devoted to BPA, the Scientific Working Group on Bloodstain Pattern Analysis (SWGSTAIN), whose mission is:
“… to serve as a professional forum in which BPA practitioners and practitioners from related fields can discuss and evaluate methods, techniques, protocols, quality assurance, education, and research relating to BPA.
SWGSTAIN began formulating guidelines for practicing BPA. Logical place to begin was to standardize the terminology to create standard way of communicating AND to minimize confusion surrounding terminology that had been adopted ad hoc over time.
Interestingly, the SWGSTAIN final version was not published until 2009, after publication of the NAS report
Scientific Basis of BPA
Scientific Basis of Bloodstain Pattern Analysis
If BPA has basis in science, testimony should be admitted into evidence Testifying expert analyst must meet appropriate standards Must have as yet undefined credentials. Understanding basis of BPA Gained through education and experimentation while employing the principles of the relevant scientific disciplines: biochemistry, fluid mechanics (dynamics), physics, chemistry, ballistics, and mathematics. These disciplines form the scientific basis of BPA, and their principles must be able to explain why blood forms the patterns it does. If cannot, then BPA does not have a basis in science and must be considered art.
The scientific basis must yet be proven
: SWGSTAIN provides references designed to document the scientific basis of BPA.
To address the topic properly, first understand the nature of blood, which requires knowledge of biochemistry.
Classification of Blood
Viscoelastic, Newtonian fluid. Understanding what happens to it after it leaves the human body, Whether acted upon by a force or just passively dripping from an object, o Requires more than casually observing bloodstain formation empirically in a workshop setting or in the field. In depth knowledge of the biochemistry of blood
Blood Composition and Surface Tension
Composition: Blood plasma composed of macromolecules (proteins, carbohydrates, water and other dissolved salts and other molecules). Its physical properties –
viscosity and surface tension
– are mainly determined by dissolved macromolecules in the blood’s plasma. Surface tension is the force that makes blood droplets (or any liquid) maintain its integral structure, Blood retains its shape until acted on by a force that overcomes the surface tension. The force that overcomes surface tension creates blood spatter and thus the patterns observed at crime scenes.
How the force is applied and its strength determines the visual appearance of the resulting pattern. To See Demonstration of Surface Tension
The laws of physics apply to blood droplets in flight
Direct application to blood droplet formation and its flight characteristics should be well understood.
These considerations have been taken for granted
Mostly from empirical studies in a workshop setting.
Few publications document whether blood flight conforms to the laws of fluid dynamics.
Fluid mechanics (dynamics). Study of fluids (liquids, gases and plasmas) and the forces acting on them.
Its laws define blood in motion after being acted on by a force.
Bloodstain spatter forms from liquid blood in motion o Fluid dynamic computations describe blood in motion The bottom line is that every drop of blood at the crime scene can and perhaps should be described mathematically. Although publications exist, such a study has not been done systematically.
A concept of fluid dynamics.
A blood droplet reaches terminal velocity (settling velocity) when speed becomes constant,
Downward force of gravity
equals upward force of drag. When a blood droplet’s speed is constant, drag equals the droplet’s weigh, and its acceleration is zero. For bloodstains falling from identical heights and having a constant weight (volume), their
Single drops of blood falling from fingertip onto smooth cardboard from various heights.
Little change in diameter beyond 7-8 ft.
When a blood droplet reaches its terminal velocity, the stain on a hard, smooth surface, will have a constant diameter, regardless of the height from which it falls. terminal velocities will be identical. Generally, terminal velocity occurs at approximately 20 feet. Experiments show that bloodstain diameters change very little after falling approximately 8 feet.
Trajectory Analysis (ballistics)
Blood leaving human body under a force forms an arc Path described mathematically. Blood droplet represents a projectile Path is its trajectory. Like a bullet, the arc a blood droplet takes to its final terminus is dependent on gravity, wind currents, temperature, humidity and friction. In real world, other considerations exist: non-uniform gravitational forces, air resistance (friction) – drag and aerodynamics, create an arc pattern that is not parabola.
One of four fundamental interactions of nature Strong and weak interactions, electromagnetism and gravitation o Where objects having mass attract one another. The force that causes objects to fall to the ground when dropped. o Keeps planets in their obits around the sun and the moon around the earth. Described by the general theory of relativity that governs the motion of inertial objects Causes dispersed matter to coalesce, When the earth and other planets formed after the Big Bang. Defines the path blood droplets take (non-gravitational influences not considered) until they interact with an object and comes to rest.
From a bloodstain perspective
, Gravity is responsible for the natural convection by which fluid flow occurs. Influence is most apparent in the visual pattern of blood present at scenes as well as the pooling and flow of blood.
Only Force Work.
Directed toward the center of the path of the moving object. Adhesive forces hold blood onto object Blood flies off object tangentially o When adhesive forces are greater than the centripetal force, This is a straight line The impact site and its angle are a direct link to the location of the object at the exact moment the blood left.
Fundamental Principles of Bloodstain Analysis (BPA)
Surface Tension and Droplet Shape
Blood Accumulates until wt>gravity Surface tension pulls vertically &horizontally to keep droplet together Settles into a Sphere
Determining the Direction of Blood Travel and Angle of Impact of Individual Droplets
Falling downward (90 o ) Forms circle, Depending on the texture of the surface (smooth, textured, dusty, etc), its edge characteristics has varying amounts and intensity of scalloping. As impact angle becomes more and more acute, stain elongates and can form a tail points in the direction droplet was traveling. In this way, it is a simple matter to determine the direction from which blood droplets in the air were moving
Adapted from Introduction to Forensic Sciences, W. Eckert, CRC, 1997 Angle of Impact
Dynamics of Droplet formation Effect of Oblique Impact
Pizzola and Deforest defined what happens to blood when it strikes an angled surface … Demonstrated mechanism of how blood interacts with a surface to form the specific patterns encountered at crime scenes
Blood or Drip Trails
According to SWGSTAIN terminology, a drip trail is, “
A bloodstain pattern resulting from the movement of a source of drip stains between two points
.” When blood drips from object in motion, the resulting droplet shapes can range from nearly circular (falling nearly perpendicular to the surface) to elongated (hitting the surface at an angle) depending on the speed of the travel. If droplets form elongated stains, direction of travel direction the stain points. The tail points toward movement of droplet. However, for objects moving slowly the droplets can be nearly circular, mimicking droplets falling from a height.
Drip Trails - Continued
Examine edge characteristics of the resulting stain,
Direction depends on texture of the interacting surface – smoothness.
Edge characteristics show direction of travel to a greater or lesser extent Texture of the interacting surface, determines degree of scalloping, presence of spines and/or associated satellite stains. o
Extremely smooth surfaces
: Edge characteristics of droplet minimal or almost o nonexistent.
Droplets have edge characteristics that are not smooth: they will have scalloping and may have spines or even satellite stains associated with them.
Direction of travel
Leading edge of stain has preponderance of spines and/or satellite stains, Pointing in the direction of the movement.
Relying on a single droplet in a drip trail to determine the direction of movement can lead to either misinterpretation. Visible scalloping on the left, suggesting it originated from someone moving right-to-left. However, edge scalloping is present on the right side of the droplet stain - in the lighter area. Confusing because concentration of blood on the left side of droplet suggests a left slant to the floor. Actually floor is horizontal Lighter colored area occurred because droplet repelled by wax on freshly waxed floor
Closer inspection of the light area shows scalloping and small satellite stains, the latter suggesting movement from left to-right. Correct interpretation Interpreting direction as moving right-to-left … incorrect.
If other stains in the trail were equally as confusing as stain in photograph, the logical interpretation would be inconclusive.
Shape & Size of Bloodstain Droplets
Shape - Target surface
texture (rough or smooth)
Affects shape of droplet Collisions with surfaces that are not flat The roughness of the surface overcomes the surface tension holding the droplet together.
Volume of the droplet Distance fallen o Little change in diameter beyond 8 feet Absorption/porosity More absorptive, better spreading of droplet into surface Thickness Thick , absorptive surface pulls droplet into matrix & keeps from spreading
T- shirt Sandpaper
Surface Characteristics & Droplet Shape
Single Droplets Falling onto Various Surfaces Spines Sattelite Stains 400 Grit Sandpaper 150 Grit Sandpaper Droplet on Wood Droplet on Velcro
Perimeter Stain: Ghosting or Skeletonization
Droplet begins to dry when landing of any surface. Over time it will dry. Drying begins from the outside edge toward the middle.
Outside edges are shallower and lose water faster than middle of droplet Brushing something across drying droplet, edges form an outline.