Blood Spatter Analysis

Blood Spatter Analysis

compiled by Prof. John MooreParkland College

Champaign, IL

“I see no more than you, but I have trained myself to notice what I see.”

Sherlock Holmes, “The Adventure of the Blanched Soldier”

How did it get there?????• “passive”

• projected– (or void of projected blood)

• transfer

The standard questions…..

• Is it blood?

• Is it human blood?

• Who is the owner of the blood?

The “new” question…..• Can the blood stain or blood stains

give additional information about the mechanism by which the blood reached the target surface?– Location– Time sequencing– Number of wounds/blows– Other individuals present

1.) Blood spatter analysis• Blood should generally stay inside of a

person. • Finding blood at the crime scene is most

likely an indication that something has happened to someone!

• Among other things, the investigators must determine: – a) is the fluid truly blood? – b) is it human blood? – c) can the blood be identified as coming from a

specific person? (Note - crimes at slaughter houses really prove difficult to analyze.)

Blood spatter analysis – cont.• Blood is found at the scene of many violent

crimes. However, violence can occur without blood loss, and the presence of blood does NOT have to indicate the commission of a crime.

• It can be “matched” to a suspect with a high degree of accuracy.

• The pattern of blood stains & spatter can tell much about exactly what happened at the scene.

Blood spatter analysis – cont.

• As an example of how blood is left at a scene, consider a scenario where someone cuts their hand while at a crime scene. In most cases they will:– Grab it (the cut hand)– Sling it (out of reaction to the pain)– Run it under water (because that is what

we have been told to do since childhood)

Grab it• This will deposit blood onto the hand

used to grab the injured hand.• In all likelihood, at some point in time

blood will be “transferred” to some environmental surface at the crime scene by this blood covered hand.

• Grabbing it will generally not stop the bleeding – so dripping will occur.

Sling it

• Slinging the blood will leave a pattern on nearby environmental surfaces.

• Such patterns can also originate from blood being slung from a moving knife or impact weapon.

Run it under water

• Running water over an bleeding injury tends to disperse the blood to a larger area if done outside of a sink, e.g., using a hose in the backyard.

• Running the water over the bleeding injury in a sink will usually leave detectable blood evidence in the sink, or the trap system of the sink.

Blood components• Blood is comprised of both CELLULAR

and LIQUID components. • The cellular elements and the liquid

component of blood are normally “mixed” – with the formed cellular elements floating in the liquid phase. (The diagram shows the two phases separated.)

Blood – separated into cellular & liquid components

Blood characteristics

• Average person has between 5-6 liters of blood

• Blood is approximately 6x thicker than water - like a thin syrup.

• Blood can both “dry” as well as “clot”. Both versions will often be seen at a crime scene.

BLOOD CLOTTING• Blood clotting is NOT the same as blood

drying.• Drying is a function of losing water.• Clotting is an active biological process

where the liquid portion of the blood (plasma) changes to a gel-like substance.

• Blood generally clots in 3 – 13 minutes, with 7 minutes being a good average.

Falling blood – “drops”

• The SHAPE of a free-falling drop of blood is roughly SPHERICAL. Note that this is unlike the classic tear-drop shape often seen!

• The blood drop will oscillate as it falls due to air resistance.

Blood drop origination

passive or gravity drop

Blood drop oscillation

• Corona effect: D/t blood falling into a pre-existing pool of blood. The pattern radiates out from the pint of impact. (When stopped via flash photgraphy, the radiating droplets look like a crown, hence the term “corona”.)

• See following slide for images of corona effect.

Stain – smooth surface

Stain – textured surface

Stain – rough, textured surface

stringing

BLOODSTAIN SIZE - The bloodstain produced by a blood drop is

PROPORTIONATE TO THE SIZE OF THE DROP.

Blood drop impact

Blood spatter

• A BLOOD SPATTER is the result of an impacting FORCE striking a STATIC pool of blood. NOTE - This is NOT called blood SPLATTER! (Another way to think of this is that “splatter” is the sound made when the blood is caused to spatter.)

• See following slide for mechanism of spatter.

Blood spatter – mechanism of formation

Blood spatter – mechanism of formation

Splash pattern

Cast-off

Blood spatter Application to crime scene evidence.

• The SPHERICAL drop of blood (regardless of source) will impact some physical structure, thus causing a BLOODSTAIN. If the drop strikes PERPENDICULAR to the surface involved, the WIDTH and LENGTH of the bloodstain will be equal, for all intents & purposes. If the drop is moving horizontally, or if the surface is not perpendicular to the path of the drop, the bloodstain will take on an elliptical or oval shape.

Things that can be determined from blood stain & pattern analysis:

• What occurred at the scene.• Who was (or was NOT) present.• How many blows were struck.• Position of victim and assailant.• Origin of the bloodstains.• Sequence of events.

Blood spatter – cont.• When seen from “above”, a stain can sometimes

resemble a tadpole or exclamation point! The “dot” of the exclamation point indicates the DIRECTION OF TRAVEL of the blood drop.

• Some drops don’t taper as much (d/t different

types of surface that they impact, or different impact angles) - and will become more “jagged” in appearance. This jagged edge is the direction of travel.

• The shape of the stain can also help determine the angle at which the blood impacted the surface.

angle of impact vs. stain shape





Spatter size

• Spatters are often lumped into categories

such as low, medium, and high velocity spatters (LVS/MVS/HVS). There is, unfortunately, a tremendous amount of variability & overlap. Due to this - pattern analysis CANNOT BE BASED UPON AN INDIVIDUAL STAIN. The MAJORITY OR PREPONDERANCE OF STAINS must be used as the basis of an evaluation.

LVS characteristics

Usually associated with activities such as:• Drops falling passively to target• Drip spatter (blood dripping into a pool of blood)• Splashed blood• Stepping into pool of blood• Large volume of blood falling at least 4 inches• LVS are usually large, d/t low applied force. (>

3mm)

Low velocity

MVS patterns

Usually associated with:

• Velocities of 5 – 25 fps

• Beatings or stabbings

• Most spatters are < 3mm in diametrer

Medium velocity

HVS patternsUsually associated with:

• Velocities in excess of 100 fps• GSWs• Explosions• Mechanical accidents involving high

speed machinery• Majority of spatters are < 1 mm

(“mist”)

HVS patterns – cont.• Dry quickly• Do not travel far• If GSW – bullet entry angle detrmines

spatter direction• Often hidden (or missed) in textured

surfaces, such as carpeting• May exhibit both backspatter &

forward spatter

Forward & backspatter

hvs

High velocity

Expiratory blood

• Expiratory blood can originated from two major locations – the nose & mouth, or from an open chest wound (commonly called a “sucking chest wound” in clinical settings.)

• If originating from the mouth, a degree of salivary dilution can occur, resulting in a blood stain that is noticeably lighter in appearance than one associated with normal blood.

Expiratory Blood The arrow points to a stain cause by

a “bubble” of expired blood hitting the target surface.

Arterial gushing

Arterial spurt

Flow change d/t movement of body relative to gravity

transfer

transfer

transfer

Transfer / sequencing

transfer

transfer

Transfer / sequencing

Uninterrupted swipe

The following are some general rules of bloodstain pattern analysis.

• The smaller the size of bloodspatters, the greater the energy required to produce them. Low, medium, and high velocity impact spatter may be identified by their respective sizes but exceptions must also one considered.

• http://www.brazoria-county.com/sheriff/id/id~top.htm

• Before a drop of blood can fall, absent any other form of applied energy, gravitational attraction acting on blood must exceed its surface tension.


• Diameter of a large bloodstain will be of little or not value in estimating the distance a drop of blood has fallen prior to impact.


• When considering the shape of a bloodstain for use in calculating its angle of impact, only a sharp, well-defined bloodstain 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 bloodstain. The pointed end indicates the direction of travel prior to impact on a surface. Directionality may also be determined when edge scallops appear on only one side of a bloodstain.


• Correct interpretation of bloodstain patterns must include consideration of the surface texture of the material upon which the bloodstains have been deposited.


• Surface tension prevents spattering regardless of the distance a drop of blood has fallen before impacting a smooth, hard surface such as glass.


• Edge characteristics of a bloodstain have no value in establishing the distance a drop of blood may have fallen prior to impacting a surface unless the nature of the surface texture is considered.


• Conclusions as to the significance of a limited number of bloodstains should only be drawn with reservations and/or qualifications. It should be remembered that a few bloodstains do not a pattern make. There is nothing wrong with admitting that there are insufficient bloodstains available to form an opinion. It is far better not to have an opinion than to have one that is incorrect.


• When a dozen or more small bloodstains are present in a recognizable pattern, their size may allow a prediction as to the energy that was required to produce them. When the preponderance of individual bloodstain diameters are less than 1mm, they are consistent with having been produced as a result of a high velocity impact. Most often they would result from a shooting.


• When the preponderance of dozens of individual bloodstains are approximately 1mm or more in diameter, they are consistent with having been produced as a result of a medium velocity impact. Most often they would result from a beating or stabbing.


• The shape of a bloodstain is a function of the angle at which it impacts a surface. Perfectly round bloodstains result from a ninety degree impact. The angle of impact of an elliptical bloodstain may calculated from its length to width ratio.


• Bloodstains may often be lifted from the surface upon which they have been deposited. The harder and smoother the surface the more likely they may be successfully lifted.


• When measurements and angles are used to establish the origin or origins in space, not only will the actual origin be somewhere below the point or points of convergence, but it must be remembered that the investigator is determining a spatial volume and not a small pint of origin.


• Sobriety of the victim will have no significant effect on how bloodstain patterns are produced. A high blood alcohol level is of no concern to the interpretation of bloodstain patterns.


• When blood is projected upward with sufficient force to strike a ceiling, it will almost always be the result of a gunshot having an upward trajectory. Such a trajectory is more often the result of a suicide rather than it is a homicide.

• An exception is when dealing with cast-off blood patterns.


Documents

Blood Spatter Analysis