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A Brief review inBlood Spatter Analysis Ahmed Almumtin, MD
What does it remind you of?• Forensic science?• OR.. DEXTER!
Blood and Life– Blood Volume • On average, accounts for 8 % of total body weight • 40% of total blood volume loss, externally or internally is usually fatal ..
What is it?• A field of forensic examination of the shapes, locations, and distribution patterns of bloodstains, in order to provide an interpretation of the physical events which gave rise to their origin.
What does it tell us?• Type and velocity of weapon• Number of blows• Handedness of assailant (right or left-handed)• Position and movements of the victim and assailant during and after the attack• Which wounds were inflicted first• Type of injuries• How long ago the crime was committed• Whether death was immediate or delayed
While a reconstruction could tell some more.. 1. Stain condition 2. Pattern 3. Distribution 4. Location 5. Directionality
Before that..• Is it really blood? How to tell? – a light source. – Blood reagents: Phenolaphthalien (Kastle myer test pink), HemaStix (tetramethylbenzedine Luminol green or cyano with Hb) Reaction – Luminol + UV light: (Blue) • Can detect blood even if cleaned or removed. • Disadvantage: can give +ve results with some metals ex. Copper, bleaching products or paints. – Flouroscine: • Useful for fine smears or stains
Terminology• Angle of impact: angle at which blood strikes a target surface• Bloodstain transfer: when a bloody object comes into contact with a surface and leaves a patterned blood image on the surfac• Back-spatter: blood that is directed back toward the source of energy• Cast-off: blood that is thrown from an object in motion• Directionality—relates to the direction a drop of blood travels in space from its point of origin• Contact stain: bloodstains caused by contact between a wet blood-bearing surface and a second surface that may or may not have blood on it Transfer—an image is recognisable and may be identifiable with a particular object Swipe—wet blood is transferred to a surface that did not have blood on it Wipe—a non-blood-bearing object moves through a wet bloodstain, altering the appearance of the original stain
• Parent Drop – The droplet from which a satellite spatter originates.• Satellite Spatters – Small drops Satellite Spatters of blood that break of from the Spines parent spatter when the blood droplet hits a surface.• Spines – The pointed edges of a stain that radiate out from the spatter; can help determine the direction from which the blood Parent Drop traveled.
Types of Blood stain patterns• Passive Bloodstains (drops, pools, etc.)• Transfer Bloodstains (wipe a weapon, etc.)• Active (or “Projected”) Bloodstains (bullets, stepping in blood, etc.)
Projected bloodstains• Projected bloodstains are created when an exposed blood source is subjected to an action or force, greater than the force of gravity. (Internally or Externally produced)• The size, shape, and number of resulting stains will depend, primarily, on the amount of force utilized to strike the blood source.
Arterial Spurt / Gush• Bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery:
Cast-off Stains• Blood released or thrown from a blood-bearing object in motion• A useful way to understand it, is to imagine yourself running while holding a cup of pomegranate juice!
Droplets could be altered..• Size of the droplet• Angle of impact• Velocity at which the blood droplet left its origin• Height• Texture of the target surface • On clean glass or plastic—droplet will have smooth outside edges • On a rough surface—will produce scalloping on the edges
Size and Velocity• Low velocity spatter is about 5 ft / second and usually 3 mm or greater in diameter and indicates blood is dripping.• Medium velocity spatter is 5 – 25 ft / second with a <3 mm diameter and usually indicates blunt trauma or sharp trauma or it could be cast-off.• High velocity spatter is 100+ ft / second with a spatter of < 1 mm indicating gunshot trauma, power tools, an object striking with extreme velocity (airplane prop) or an explosion, may be referred to as fly specks.
ImpactThe more acute the angle of impact, the more elongated the stain.90-degree angles are perfectly round drops; 80-degree angles take on a more elliptical shape.At about 30 degrees the stain will begin to produce a tail.The more acute the angle, the easier it is to determine the direction of travel.The shape of a blood drop: Round—if it falls straight down at a 90-degree angle Elliptical—blood droplets elongate as the angle decreases from 90 to 0 degrees; the angle can be determined by the following formula:
Surface and ShapeMedium impact occurs when a force Low impact is really blood under thesuch as a bat is applied. influence of gravity - it just falls.
High impact - fine mist of droplets Image courtesy Stuart James, February 2007
Stage 1: contact & collapseImage used with permission from Tom Bevel & Ross Gardner, June 2006.
Stage 2: displacement Image used with permission from Tom Bevel & Ross Gardner, June 2006.
Stage 3: dispersion Image used with permission from Tom Bevel & Ross Gardner, June 2006.
Stage 4: retraction Image used with permission from Tom Bevel & Ross Gardner, June 2006.
Target surface texture• Blood droplets that strike a hard smooth surface, like a piece of glass, will have little or no distortion around the edge.• Blood droplets that strike linoleum flooring take on a slightly different appearance. Notice the distortion (scalloping) around the edge of the blood droplets.• Surfaces such as wood or concrete are distorted to a larger extent. Notice the spines and secondary or sentinel spatter present.•
Size or volume of droplets• Large volumes of blood (patterns created by same volume of blood, from same source to target distance) "Dripped Blood" "Spilled Blood"
Impact Spatter• Blood stain patterns created when a blood source receives a blow or force resulting in the random dispersion of smaller drops of blood.This category can be further subdivided into; Low Velocity Gravitational pull up to 5 feet/sec.Relatively large stains 4mm in size and greater
Directionality sin θ = W / LWhat does W = L mean?sin θ = 1 → θ = 90Drop is a circle!
one exception!tail points in direction of travel
And from Dexter ;-)• The common point, on a 2 dimensional surface, over which the directionality of several bloodstains can be retraced.• Once the directionality of a group of stains has been determined, its possible to determine a two dimensional point or area for the group of stains.• By drawing a line through the long axis of a group of bloodstains the point of convergence can be determined. Where the lines of the group of stains intersect one another the convergence point can be established.
Continue Directionality• When considering the shape of a blood stain for use in calculating its angle of impact, only a sharp, well-defined blood stain should be used for measuring its width and length• Directionality of a blood drop while in flight is usually obvious from the geometry of its resulting blood stain – The pointed end indicates direction of travel of the drop prior to impact on a surface – Direction of travel may also be determined when edge scallops only appear on one side of the stain
• A few blood stains do not make a pattern• Draw conclusions with reservations and/or qualifications• It is ok to admit that there is insufficient evidence to draw a conclusion from BPA• No opinion is better than an incorrect, forced opinion
• When the preponderance of individual bloodstain diameters are less than 1mm, they are consistent with having been produced as the result of high velocity impact (most often shooting)
• When the preponderance of individual bloodstains are 1mm or more in diameter, they are consistent with having been produced as the result of medium velocity impact (most often beating or stabbing)
• The shape of a bloodstain is a function of the angle at which it hits/impacts the surface• Perfectly roundninety-degree impact/drop angle• Angle of impact of elliptical drop may be determined using length to width ratio of the drop