1 Origins of bloodstain 2 Distance of bloodstain
1) Origin(s) of bloodstain 2) Distance of bloodstain from target 3) Direction from which blood impacted
4) Speed with which blood left its source 5) Position of victim & assailant 6) Movement of victim & assailant 7) Number of blows/shots
§ On average, blood accounts for 8 % of total body weight § 5 to 6 liters of blood for males 4 to 5 liters of blood for females
§ A 40 percent blood volume loss, internally or/and externally, is required to produce irreversible shock (death). § A blood loss of 1. 5 liters, internally or externally, is required to cause incapacitation ( unable to function).
§ More rapid bleeding may result in slightly larger drops. § BUT, on the contrary, slower bleeding does not result in smaller drops.
§ Blood cast from a moving source will tend to consist of smaller droplets. § Blood behaves as a projectile in motion and obeys the laws of physics and mathematics.
n. PASSIVE n. TRANSFER n. PROJECTED
DEFINITION: drops created or formed by the force of gravity acting alone.
EXAMPLES: Drops Drip Patterns Pools Clots
PICTURES:
DEFINITION: created when a wet, bloody surface comes in contact with a secondary surface.
EXAMPLES: Contact bleeding Swipe or Smear Wipe Smudge
PICTURES: All or a portion of the original surface may be observed in the pattern.
DEFINITION: created when an exposed blood source is subjected to an action or force, greater than the force of gravity.
EXAMPLES: Arterial Spurt / Gush Cast-Off Impact Spatter
PICTURES:
“Fitting” of an ellipse in blood drop Tail or spine Parent Drop
Low Velocity Medium Velocity High Velocity
LOW VELOCITY Relatively large stains 4 mm in size and greater. Gravitational pull up to 5 feet/sec.
MEDIUM VELOCITY Stain size 1 to 4 mm in size. Force of 5 to 25 feet/sec.
HIGH VELOCITY Stain size less than 1 mm Force of 100 feet/sec. or greater.
ANGLE of IMPACT is the angle formed between the path of a blood drop and the surface it strikes.
By utilizing trig functions, it’s possible to determine the impact angle for any given blood droplet.
By accurately measuring the length and width of a bloodstain, the impact angle can be calculated using the SIN formula below: AOI = -1 SIN W /L
Finding AOI LENGTH = 5. 9 cm WIDTH = 2. 6 cm
SOLUTION: AOI = SIN-1 W / L AOI = -1 SIN 2. 6/5. 9 AOI = SIN-1 (. 44) AOI = 26. 2°
45○ ANGLE 10○ ANGLE 30○ ANGLE 5○ ANGLE
DEFINITION: The common point, on a 2 dimensional surface, where the direction of several bloodstains meet
Once the directionality of a group of stains (one or two stains is not sufficient) has been determined, it's possible to determine a 2 D point (or area) where the group of stains meet.
By drawing a line through the long axis of a group of bloodstains, the point of convergence can be determined. LONG AXIS / LENGTH
Point of Convergence (2 D)
DEFINITION: The location in 3 -D space where the blood produced originated. Measurement of the impact angle allows for translation of the 2 -D image (convergence) into a 3 -D one (origin).
TO DETERMINE WHERE THAT POINT IS LOCATED: 1) First measure the distance from each blood stain along its central axis to the POC (distance = y) 2) Then take the TAN of the degrees AOI.
3) Third, multiply the TAN of the AOI by the distance. 4) Measure that distance from the floor up the perpendicular axis and you will arrive at the Point of Origin (PO) FORMULA: PO = TAN (AOI) x y
Finding PO GIVEN: DISTANCE FROM BLOODSTAIN (to POC): 90 cm AOI (calculated from AOI formula): 30° SOLUTION: PO = TAN (30°) x 90 cm PO =. 577 x 90 cm = 52 cm
Point of Origin (3 D --- use Z axis)
In practice (at a crime scene), strings, tapes and protractors are commonly used.
Computer programs can also be used.
The spherical shape of blood in flight is important for the calculation of the angle of impact (AOI) of blood spatter when it hits a surface.
When a droplet of blood strikes a surface perpendicular (90 degrees) the resulting bloodstain will be circular. The length and width of the stain will be equal. 90○ ANGLE
Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape. 70○ ANGLE
§ Experiments with blood have shown that a drop of blood tends to form into a sphere in flight rather than the artistic teardrop shape. § The formation of the sphere is a result of surface tension that binds the molecules together. § This elastic like property of the surface of the liquid makes it tend to contract.
- Slides: 44
