In order to analyze bloodstains present at a crime scene, we must first classify each one. Classifying a bloodstain or pattern must be based on the physical characteristics of the stain or pattern. It is important to remain objective when classifying stains. Bevel & Gardner introduce the idea of using a taxonomic classification system in order to reduce subjectivity. In this class, we will use the Taxonomic Classification System for Bloodstains in order to classify bloodstains. You can also use the Decision Map provided in the e-book to assist in using the Taxonomy.
We start with Bloodstain. Is the stain actually blood? We will learn next week, how to test stains to determine if in fact the stain is blood.
Once we determine the stain is blood, we then have to decide if the stain is a Spatter Stain or Non-Spatter Stain. It is important to observe the stains objectively and not base your interpretation of the stain on any theories presented about the crime and crime scene.
Common characteristics of all spatter stains are that they are elliptical or circular shaped (contain scallops, spines or a tail and secondary/satellite spatter), resulting from free-flight of blood impacting the surface.
Linear Spatter (linear orientation)
Arterial Spurt – linear, large volume, long stains
Cast-Off – linear, no large volume, progressive, consistent impact angle change Drip Trail – linear, no large volume, lead from one point to another
Non-Linear Spatter (no linear orientation)
Impact Spatter – pattern has radiating distribution, progressive change in shape
Expectorate Spatter – pattern has radiating distribution, bubble rings or mucous
Drips – No pattern, random oriented on the surface
Primary stain is not spatter, in other words, not created by free-flight of blood impacting the surface.
Irregular Margin – Non-Spatter (irregular or spiny margin)
Gush/Splash – large volume, large irregular stain, secondary spatter (spiny margins)
Blood into Blood – large volume, irregular margin, random spatter around margin
Smear – feathered boundary, striations in stain, diminished volume, no spatter
Wipe – a smear stain, displaced blood from original stain, no spatter
Swipe – a smear stain, no original stain, created by bloody object, no pattern Regular Margin – Non-Spatter (regular margin)
Pattern Transfer – contact pattern, recognizable object that deposited blood
Pool – large volume, conforms to surface contours, serum separation or clotting
Saturation – no specific shape, absorbed into permeable surface
Flow – movement with surface contours, margins lead from one point to another
Basic reproducible bloodstain pattern types
Blood dispersed from a point/area by a force (i.e., impact patterns, expectorate) Bloods ejected over time from an object in motion (i.e., cast-off patterns) Blood ejected in volume under pressure (i.e., spurt or gush patterns) Blood dispersed as a function of gravity (i.e., drip patterns, drip trails) Blood accumulates and/or flows on a surface (i.e., pools, flows) Blood deposited through contact transfer (i.e., smears, pattern transfers)
The scientific method provided a methodical, objective way to answers questions. The method is cyclic in that if the hypothesis is incorrect then you do it again:
Ask a question Gather data Construct a hypothesis Test your hypothesis via experiment Analyze results & draw conclusion Report your results. Was your hypothesis correct? If not, try again!
How do we apply the scientific method to BPA? The following is the 8-step methodology prescribed by Bevel & Gardner (2008):
Become familiar with the crime scene. Identify the discrete patterns among the many bloodstained surfaces. Classify these patterns based on taxonomy. Evaluate aspects of directionality and motion for the pattern. Evaluate angles of impact, points of convergence, and areas of origin. Evaluate interrelationships among patterns and other evidence. Evaluate viable source events to explain pattern, based on all evidence. Define a best explanation of the events.
Motion & Directionality of Bloodstains
Determining motion and directionality of a blood droplet can assist analysts in understanding what happened at a crime scene.
Bevel and Gardner (2008) highlight three key points about motion:
1. General direction of events – the area where the least amount of blood is present is generally the beginning of the event because blood will flow more freely with time or as the victim is repeatedly injured and as the victim moves around.
2. Droplet directionality – in many instances, the direction of a droplet upon impact on regular surfaces can be determined by looking at the location of spines, satellite spatter, scallops, and tails. For example a scallop located on the east side of a droplet indicates that the droplet was traveling from the east.
3. Recognizing blood trail motion – as an injured person moves, blood will drop from the wound(s). The droplets will have forward momentum. As the injured person increases speed, the droplets will become more elliptical in shape upon impact. It is also important to look for the presence of spines, satellite spatter, scallops, and tails which will assist in determining the direction of the blood trail. It is important to analyze the trail as a whole and not just focus on one droplet.
Determining motion from wipe & swipe stains: Thinning of the blood volume can is a good indicator of direction.
How can impact pattern stains help analysts what caused the stain?
First, we have to understand that impact spatter is caused when an outside force (blunt object, gunshot) strikes a blood source. Impact spatter has a radiating pattern upon contact with a surface. Spatter stains differ in their size. It is important for an analyst to describe those characteristics.
There are several methods to describe impact spatter stains. Impact velocity is method in which bloodstains are categorized by velocity groupings: low- velocity (LVIS), medium-velocity (MVIS), and high-velocity (HVIC). LVIS (results of gravity) are larger stains in comparison to MVIS and HVIS (results of gunshot wounds).
It is important for analysts to determine the preponderant stain size (the most common stain within a pattern).
Impacts from outside sources result in smaller droplets. The center of the radiating impact pattern is the point where the impact occurred. The presence of gunshot spatter can provide investigators with clues about what happened at the crime scene. Forward spatter – only present when bullet exits victim, flows in direction of bullet. Back spatter – flows back from direction of bullet, possibly onto shooter if in close range of the victim.
Proper documentation of bloodstains include: detecting and collecting bloodstain evidence, photographing and video recording bloodstains, sketching bloodstain patterns, and writing reports about every action taken in regards to the bloodstains.