Sunday, May 13, 2012

Bloodstain Pattern Analysis


Bloodstain Pattern Analysis is the examination of the shapes, locations, and distribution of patterns of bloodstains, in order to provide an interpretation of the physical events that gave rise to their origin.
Terms used in Blood Stain Pattern Analysis
1.      Angle of Impact: the angle at which a blood droplet strikes a surface
2.      Arterial Gushing: the large pattern of blood that is created when blood escapes an artery under pressure; the increase and decrease in blood pressure is apparent
3.      Arterial Spurts: large patterns created under pressure, but with less volume and usually more distinctive evidence of blood pressure rising and falling
4.      Clot: a mass of blood and other contaminants caused through clotting mechanisms
5.      Cast-Off Stains: blood that has been thrown from a secondary object (weapon or hand) onto a target other than the impact site
6.      Drop Patterns: characteristic patterns present when blood drips into standing, wet blood
7.      Expiratory Blood: blood which is spattered onto a target, as a result of breathing; typically, this occurs when an injury is sustained to the throat, mouth, or airway
8.      Impact Site: usually the point on the body that received the blow or applied force, from which the blood was shed
9.      Origin: the point in space where the blood spatter came from
10. Parent Drop: the droplet from which satellite spatter originated
11. Projected Blood: blood under pressure that strikes a target
12. Satellite Spatters: small drops of blood that break off from the parent spatter when the parent droplet strikes a target surface
13. Shadowing/Ghosting/Void: a pattern that helps to place an object or body in the scene; normally, the area in question lacks blood even though areas surrounding it show blood
14. Skeletonized Stain: the pattern left when an object moves through a partially dried stain, removing part of the blood, but leaving the outline of the stain intact
15. Spatter: bloodstains created from the application of force or energy to the area where the blood is
16. Spines: the pointed edges of a stain that radiate out to form the spatter
17. Splash: pattern created when a volume of blood in excess of 1 mL strikes a surface at a low to medium velocity
18. Swipe: the transfer of blood onto a target surface by a bloody object that is usually moving laterally
19. Transfer Pattern: the pattern created when a wet, bloody object comes in contact with a target surface, leaving a pattern that has the features of the object making it useful for identifying the object
20. Target: the surface where the blood ends up
21. Wipe: pattern created when a secondary target moves through an existing wet blood stain on some other object
Information obtained from a proper Bloodstain Pattern Analysis

1. Distance from the blood source to the target
2. Direction of travel and impact angles
3. Nature of the force used to cause the bloodshed
4. The object used to cause the bloodshed
5. Sequencing of multiple bloodshed events
6.Interpretation of contact or transfer patterns
When properly documented, bloodstain patterns found at the crime scene, or on a particular person's clothing, can be used to:
1. Confirm or refute the position of a victim, witness, suspect, or defendant
2. Determine if there is evidence of a struggle, or if the assault is "one sided"
3. Confirm or refute statements made by principles in the case: i.e. are stain patterns on a particular person's clothing consistent with accounts given by the victim, witness, or defendant?

The simplest type of blood spatter analysis is determining spatters from transfers. Spatters are created when blood is acted upon by force, and travels through the air before landing on a target surface. Transfers occur when a blood source comes in direct contact with a target surface area.

  • Blood that falls at the speed or force of normal gravity
  • These spatters usually fall from an open wound, or from a  surface that is saturated with blood
  • The majority of the Low Force Impact Spatters are large,  circular, spatters with diameters of 4mm or more
  • Low Force Impact Spatters will increase in size as the  distance fallen increases, however, the size of the spatters  will remain constant after approx. 4 feet

  • Produced with more energy or force than gravity
  • The force of the impact causes the blood to break into  smaller size spatters  relative to the amount of  force applied
  • This type of spatter is usually seen in blunt force, stabbings,  and secondary spatters
  • Produced when the majority of larger drops of blood are  broken into smaller spatters with diameters of 2 – 4 mm
  • The force associated with this type of spatter is greater than  25 ft. per second

  • Impact spatter that measures less than 2mm in  diameter
  • The force necessary to produce this size spatter  is greater than 100 ft. per second
  • This type of spatter is usually associated with  gunshots, explosions, and high speed collisions
  • High Force Impact Spatter takes on a "mist like"  appearance

It is important to note that the term "Velocity" does not measure the speed at which the blood is traveling, but rather is used to describe or measure amount of force applied to the blood, to cause it to spatter.
Blood will not break up unless it is acted upon by force. The force must be great enough to overcome the surface tension of the blood

Blood forms a spherical shape (perfect circular shape) almost immediately upon separating from the blood source. The spherical shape is caused by the surface tension of the blood.

Surface Tension causes the blood drop to pull itself in; both horizontally and vertically. The blood drop will settle into a spherical shape, as a result of the surface tension.

The surface tension will maintain the sphere shape of the blood drop until it impacts with the surface.

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