Blood Spatter Analysis compiled by Prof. John MooreParkland CollegeChampaign, 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 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 Atear-drop@ shape often seen! • The blood drop will oscillate as it falls due to air resistance.
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.
BLOODSTAIN SIZE - The bloodstain produced by a blood drop is PROPORTIONATE TO THE SIZE OF THE DROP.
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 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.
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)
MVS patterns Usually associated with: • Velocities of 5 – 25 fps • Beatings or stabbings • Most spatters are < 3mm in diametrer