Lecture 4 - Introduction to Bloodstain Pattern Analysis (BPA) Flashcards
BPA is the study of
the shapes, sizes and locations of bloodstains in association with knowledge of the underpinning sciences (physics, mathematics and biology) to provide information on the event or a sequence of events that resulted in the deposition of these bloodstains or bloodstain patterns.
the interpretation of bloodstain pattern present at violent crime to help reconstruct the events that occurred during the commission of a crime
How physics comes into play with BPA
Look at physical characteristics, look at how blood behaves specifically since it is a liquid know that they have surface tension and viscosity so they follow the laws of physics and if a external force is applied to them then they act based on the laws of physics
Laws of physics are reproducible and reliable
BPA may provide valuable information about …
WHAT occurred during the course of the crime and the order in which these events took place.
Recording of BPA
It is essential that all bloodstains present at a crime scene are recorded by an appropriate combination of notes, sketches, photographs and/or video footage before they are disturbed by the investigators
Bloodstain interpretation …
Interpretation of bloodstain patterns can be undertaken in various locations:
at a scene (indoor, outdoor, vehicle, on a body), - Most BPA occurs at the crime scene
in the laboratory (e.g. clothing, footwear, weapons) - Items that can be removed from scene can be taken to laboratory - lab examination is more in depth/detailed, more equipment, better lighting and time in the laboratory environment
The items usually looked at in the lab are the weapons, clothing, footwear
from photographs
Dependent on the quality
Depends on whether the analyst can interpret the images
This is an area of forensic analysis that is likely to improve and become more prominent with the constant improvements in technology
Using the rules of physics, bloodstain pattern evidence can determine …
Area of origin(s) of blood
Distance between target surface and origin of blood
Type and direction of impact that produced bloodstains
Can look at the trajectories of the bloodstains
How many blows/shots (or a minimum number)
Position of bleeder during bloodshed
Movement of bleeder
Can trace the movement of the bleeder - whether they were dragged, walked away, ran etc
Sequencing, when different stains are deposited
If there are multiple patterns you can sometimes figure out which patterns came first
Obtain pertinent stains for further analysis (DNA)
Takes time and expensive to taxpayers, need to determine the best patterns to analyse for the most efficient and effective use of equipment
DNA analysis answers the question -
WHO?
- The improvements of DNA analysis has really changed the landscape for forensic scientists
BPA helps answers the question -
WHAT?
‘what happened’ is usually in contention rather than who, this is why blood pattern analysis is important because it can help piece together the series of events that took place
Bloodstain pattern analysis can be of great use in many forensic scenarios, for example:
Determining the cause of an unexplained death (homicide/suicide/accidental)
Body is at ‘odds’ with scene
Blood stain patterns may indicate the body has been moved from the original position where the blood had been deposited
Assessing claims by witnesses and accused
See if there is support for a particular story or not
Defence of suspect is ‘self defence’ or ‘helpful bystander’
Two or more persons have bled at scene
BPA can be useful to determine the main bleeder
Might be able to identify blood from the offender which is really important
Multiple blood patterns observed
Bloodstain =
any deposition of blood on a surface
blood stains often occur in groups =
bloodstain pattern
Pattern usually indicates that these bloodstains have come from the same event e.g. same blow
Terminology determined now by …
In 2017 these were updated by the OSAC Bloodstain Pattern Analysis subcommittee
8 scientific method steps for BPA
These 8 steps are very important and outline the scientific method
BPA is quire objective and scientific
- Scene/item overview
- Locating blood
- Documentation/record observations
Step 3 is about collecting the data
Recording and measuring - Analysis of elliptical stains
Mathematical analysis - Placing stains into groups
Use the analysis to do this - Classification and Interpretation
- Formulate hypothesis and theories
- Form conclusions
Step 1 - scene/item overview
Define boundaries of examination
How big is the job? - determine the resources and manpower required
Make sure the expectations for the scene are communicated properly
Document conditions
Memory unreliable, so notes are very important - can give evidence much later in time such as years in the future so having a record of important details is essential
Limit contextual information to minimise biasing effects
Go in with an open mind when doing scene examination
Step 2 - Locating
Search and identify visual stains
Visually identify and then can do chemical tests for blood thats hard to
Use presumptive chemical tests for confirmation
Low power stereo microscope
Helpful for very small traces of blood such as blood caught in shoe tracks or in a watch strap
Search for non visible blood with enhancements NIR (near infared) camera - Useful dark coloured objects where blood is believed to be where you can’t see contrast, Non-destructive so useful however its effectiveness is dependent on the dyes in the fabric Chemical enhancements (eg luminol) - These cause a chemical reaction (usually a colour change)
Luminol examination
A chemical reagent which reacts with traces levels of blood to produce a chemiluminescent reaction.
Spray reagent onto the surface
Chemical reaction so it is destructive and it reacts with traces levels of blood if present after being sprayed onto the surface of interest
Light is emitted if blood is present therefore the testing has to be done in the dark
The reaction must be viewed in the dark making documentation difficult.
Have trained photographers so that documentation can still occur
Very sensitive but the least specific chemical test for blood. False positives can occur
Training and experience are required to interpret the results.
Luminol can be used at scenes where blood is suspected to be present and:
Trace (non-visible) levels are anticipated
Clean up of blood is suspected
Movement of body/objects e.g. dragging of body
Patterns may be present e.g. footwear, footmarks
Note - Luminol works better on more oxidised stains
Step 3 - recording observations
The number of bloodstains - Could be a few, hundreds or thousands
Location
Size
Shape (including directionality) - Shape can tell us the direction that the droplet was travelling when it landed
Colour and intensity of blood within stain - Could be one colour, could be darker in some areas and lighter in others dues to the deposition of blood
Spatial relationship between bloodstains
Spatial relationship between bloodstains and other objects or surfaces nearby
Alteration/disturbance of different stains
The surface characteristics of the material (target) upon which stains are deposited- Is the surface absorbent? Soft? Smooth? - influences how the blood behaves when it lands and therefore how the stain looks
Step 4 - Analysis of elliptical stains
variation in shape with impact angle … As the angle decreases (from 90 towards oblique) the length increases —> stains become more elliptical = W:L ratio decreases—> when you graph this you can find out the predicted path trajectory (which follows the sine law)
area of origin determination
Elliptical stains are the result of …
small droplets of blood that land on a surface, they spread as they land and collapse, if they land straight down then they will spread evenly to a circle but if it lands on an angle then it forms an elliptical shape
Direction of elliptical stains
Nose’ of the stain indicates the direction of the stain
As the droplet collapses, the direction that the droplet is travelling can sometimes force a wave cast off to lift up off the main stain and then form this spine or tail (really should be called a nose because it is coming off the front) and it points to the direction that the blood is travelling
These spines are really useful for determining direction of the stains
Angle of landing of the blood stain and its effect on the elliptical shape
The ellipses have a width and a length, and this can change
At 10 degrees it is a very long and thin stain
At 60 degrees the blood stain is more circular
Elliptical stains - variation in shape with impact angle
As the angle decreases (from 90 towards oblique) the length increases —> stains become more elliptical = W:L ratio decreases—> when you graph this you can find out the predicted path trajectory (which follows the sine law)
Elliptical stains - area of origin determination
Combining the directionality of selected stains with their angle of impact, the straight line trajectory can be estimated
Step 5 - Placing stains in group
Identify evidence of an association between the stains (common characteristics):
Same location
Similar size/size range
Shape of stains (including directionality)
Originate from common area (share 2D or 3D convergence)
Overall shape/distribution of stains (radial, linear, curvilinear)
Step 6 - classification of bloodstain patterns
There are 3 primary classification groups for bloodstain patterns:
(These classification are based on the mechanisms of how the bloodstains were created)
1) Passive Stains (caused by gravity)
Caused by gravity and bleeding alone
2) Spatter Stains (caused by an external force)
Extra force is applied to liquid blood which has caused it to form little droplets which then go on to form circle and elliptical stains
3) Transfer Stains (caused by contact)
You have blood on an object and it makes contact with another surface which causes it to create a transfer stain
3 classifications of blood stain patterns
passive stains
spatter stains
transfer stains
passive stains caused by
gravity
caused by gravity and bleeding alone
spatter stains caused by
an external force
Extra force is applied to liquid blood which has caused it to form little droplets which then go on to form circle and elliptical stains
transfer stains caused by
contact
You have blood on an object and it makes contact with another surface which causes it to create a transfer stain
active stain
Active bloodstains are defined as those caused by blood that may have been made to travel by a force other than that of gravity such as impact to the body of a victim by a fist and/or weapon OR protection of pressurised blood onto a surface
i.e. active stains are spatter stains and transfer stains
characteristic feature of projected pattern
projection of pressurised blood onto a surface (volume of blood issuing from a punctured artery under pressure may be large (known as gushes) or relatively small (termed spurts) and the overall pattern of these projected bloodstains may clearly reflect the rise and fall of blood pressure in the arteries and the present of spines (i.e. linear stains) is also characteristic of this type of active bloodstain and is caused by the volume of blood involved and the pressure under which the blood is projected)
characteristic feature of cast off pattern
one that emanates from a secondary objects that is soaked with blood such as the weapons used in an attacking blood may be flung off the object as it is moving or as a result of a sudden cessation in its motion, stains created in this fashion are sometimes referred to as cast off stains (the cast off pattern produced is characteristically composed of individual drops of blood distributed along a line. This line may be curved or straight depending on the circumstance of its deposition. By examining such bloodstain patterns, it may be possible to deduce the minimum number of times that a victim has been struck, as each line corresponds to at least one strike.
direction of travel may be discerned from the direction in which tails of the individual stains point (this is usually the same as the direction of travel of the blood droplets) … EXCEPTION =
stains created when a larger droplet of blood impacts on a surface therefore throwing off smaller droplets. The tail of these smaller, ‘satellite’ stains point towards the parent drop. It is therefore important to distinguish between parent and satellite stains when interpreting the direction of travel
As the angle of impact decreases,
as the angle of impact decreases, the shape of the resultant bloodstain becomes progressively more elongated.
Secondary classifications of passive blood stains list
Drip stains
drip pattern
flows/flow pattern
saturated, pooling stain
Secondary classifications of passive blood stains - drip stains
A bloodstain resulting from a falling drop that formed due to gravity.
Typically result from a bleeding injury or blood falling from an object with lots of blood on it
Target can result in different presentation of the bloodstain e.g. on the corrugated cardboard is quite a non-porous surface so the blood will spread over it and spread out to cause a large stain but it is also rough so it causes splashing when the blood droplet lands and it breaks up which causes little spines and satellite stains around the outside vs on the carpet the blood falls into the 3D matrix and is absorbed into the material and blood splattering is limited/stopped from spreading with dampens the splashing as well
Passive bloodstains: Drip trail
A bloodstain pattern resulting from the movement of a source of drip stains between two points.
A trails of drip stains might all be related to the same event and just look different because of a change in surfaces throughout the trail
Directionality may sometimes be established from the stain shape and edge characteristics
Drip stains with movement of source or target, can determine speed of source or target
Walking faster gives more prominent spines
Secondary classifications of passive blood stains - drip pattern
A bloodstain pattern resulting from a liquid that dripped into another liquid, at least one of which was blood.
When blood is dripped and drips onto older stains to create a pattern since the different stains start to overlap
Usually blood into blood, but could be blood into another liquid on a surface or water etc dripping into blood on a surface
Can dilute the amount of blood if it is a liquid other than blood dripping onto the bloodstain
Central stain and then small satellite stains from the splashing effect
Secondary classifications of passive blood stains -flows/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
When blood deposits on a surface and the adhesive forces on that surface mean that the blood cannot hold there so flows in the direction of gravity instead creating a flow pattern
Useful for sequencing object positioning e.g. with the bloodstain on the heater, if it was found lying on its side then a forensic scientist would be able to say that the heater was upright when the bloodstain was deposited because of the flow of gravity
Secondary classifications of passive blood stains -saturated, pooling stain
Saturation stain - A bloodstain resulting from the accumulation of liquid blood in an absorbent material.
Pooling stain = on a non-absorbent surface such as Lino flooring
Indicates that the person has been in this position for a reasonable amount of time since there is a large amount of blood in the same area –> May help to reveal information about the length of time that has passed since the blood shed occurred, this is because drying times may be estimated
Passive bloodstains - drip trail
Passive bloodstains: Drip trail
A bloodstain pattern resulting from the movement of a source of drip stains between two points.
A trails of drip stains might all be related to the same event and just look different because of a change in surfaces throughout the trail
Directionality may sometimes be established from the stain shape and edge characteristics
Secondary classifications of spattered stains list
impact expiration arterial pressure Cast off firearms
Secondary classifications of spattered stains - impact
A bloodstain pattern resulting from an object striking liquid blood.
Stationary source of blood being hit and then the blood spreads out from here
Can have larger stains because of overlapping of blood stains due to the impact creating similar flight paths for the blood
Blood is incompressible which means that when it is struck it cannot get smaller and it has to go somewhere
Not an instantaneous process of blood stain making, it is a dynamic process because the none of the forces are in equilibrium
Can have a radial distribution due to the drag and having droplets flying through the air which slows them down
spatter stains in more depth
Spatter Stains (caused by an external force) = bloodstain resulting from a blood drop dispersed through the air due to an external force applied to a source of liquid blood. Spatter stains are typically small and elliptical/circular in shape.
Spatter stains are formed from droplets of blood in flight
Created in response to a force applied to the blood
Resulting pattern is dominated by small circular and elliptical stains
Secondary classifications of spattered stains - expiration
A bloodstain pattern resulting from blood forced by airflow out of the nose, mouth, or a wound.
e.g. coughed blood (not very diluted, large volume of blood in mouth and coughed out hence its consistent colouring unlike other airway blood stain patterns)
Anything to do with force from the airways
Often diluted if comes out airways i.e. nose and mouth, usually indicated by a darker outline around the blood stain (coffee rim effect***)
Expirated blood is complicated and varied
Secondary classifications of spattered stains - arterial pressure
( a projected bloodstain pattern, similar to hydraulic pressure that causes blood to be spattered)
A type of projected spattered bloodstain: A bloodstain pattern resulting from the ejection of a volume of blood under pressure. e.g arterial breach
High pressure causing the blood to be splattered
Often get serpentine arcs for the trajectory because of the way the heart beats and the changing blood pressure of the blood during a heart beat
The droplets are often quite large anyway but as they break up along the line of blood they start going on top of each other and cause flow patterns which is quire characteristic
Secondary classifications of spattered stains - cast off
A bloodstain pattern resulting from blood drops released from an object due to its change in motion.
Centripetal force is at play in these types of bloodstains
The faster you swing, the more blood that will come off (therefore a larger amount of blood on the blood stains will be seen)
Usually from crimes when someone is using an object to beat someone
Result of either an object being flung or an object stopping suddenly in motion and the blood is released from the object
Cast off - left to right directionality, following an object’s swing
Cast off and impact patterns are often found together because beating someone (causing impact to their body) usually involves an object or their fist which needs to be swung to cause the most damage therefore causes flinging of the blood and creates a cast off blood stain pattern
Secondary classifications of spattered stains - firearms
Own category because although it could be classified as impact, the gases in firearms can expand and impact the blood by atomising the blood
Secondary classifications of transfer stains list
pattern transfer
wipes
swipes
Secondary classifications of transfer stains - pattern transfer
A recognisable mirror image or at least a recognisable portion of the original surface may be transferred to the second surface.
Mostly hands, fingerprints and footprint marks
Sometimes there can even be enough detail to do analysis of these surfaces
Secondary classifications of transfer stains - wipes
An altered bloodstain pattern resulting from an object moving through a pre-existing wet bloodstain.
Already have blood on a surface and something clean comes through the blood and changes it
The key here is that the blood circumferences skeletonise and there are characteristic drags of the wet blood from the centre of the stains
Secondary classifications of transfer stains - swipes
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.
e.g. bloody hand to light switch, bloody hand to handrail
Opposite of wipe
Swipe =
transfer stain secondary classification
Wipe =
transfer stain secondary classification
pattern transfer =
transfer stain secondary classification
impact =
spatter stain secondary classification
expiration =
spatter stain secondary classification
arterial pressure =
spatter stain secondary classification
cast off =
spatter stain secondary classification
firearms =
spatter stain secondary classification
drip stain =
passive blood stains secondary classification
drip trail =
passive blood stains secondary classification of drip stain but in a line
drip pattern =
passive blood stains secondary classification
flows/flow pattern =
passive blood stains secondary classification
saturation =
passive blood stains secondary classification
pooling =
passive blood stains secondary classification
summary of the scientific method for BPA (6 steps)
- Scene/item overview
- Locating blood
- Documentation/record observations
- Analysis of elliptical stains
- Placing stains into groups
- Classification and Interpretation
Important to remember that to all of the blood present at a violent crime scene does not necessarily
belong to the victim
Levels of BPA (training levels)
Level 1 - The searching for stains that can be identified as blood
Level 2 - The evaluation of the physical appearance of a bloodstain and its primary classification
Scientific support staff at ESR can do this
Level 3 - The combination of the physical appearance and knowledge of the behaviour of blood allows a consideration of possible transfer mechanism and a secondary classification of the bloodstain
Advanced training, start doing classifications of mechanisms like impact and cast off
Level 4 - An evaluation of the case facts, witnesses’ testimony, crown and defence assertions leads to the development and testing of reconstruction theories
Can train others, experts
Level 1
Level 1 - The searching for stains that can be identified as blood
Level 2
Level 2 - The evaluation of the physical appearance of a bloodstain and its primary classification
Level 3
Level 3 - The combination of the physical appearance and knowledge of the behaviour of blood allows a consideration of possible transfer mechanism and a secondary classification of the bloodstain
Level 4
Level 4 - An evaluation of the case facts, witnesses’ testimony, crown and defence assertions leads to the development and testing of reconstruction theories
