1. BLOOD
SPATTER
ANALYSIS
CP Forensics
Alvarado

2. 1) Origin(s) of bloodstain 2) Distance of bloodstain from
How A SOURCE OF
FORENSIC EVIDENCE?
1) Origin(s) of bloodstain 2) Distance of bloodstain from
target 3) Direction from which blood
impacted

3. 4) Speed with which blood
left its source 5) Position of victim &
assailant 6) Movement of victim &
assailant 7) Number of blows/shots

4. On average, blood accounts for 8 % of total body weight
PROPERTIES OF BLOOD
BLOOD VOLUME
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

5. loss, internally or/and externally, is required to
BLOOD VOLUME (con't)
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.

6. SURFACE TENSION 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.

7. More rapid bleeding may
result in slightly larger
drops.
BUT, on the contrary,
slower bleeding does not
result in smaller drops.

8. 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.

9. “Fitting” of an ellipse in blood drop
Tail or spine
Parent Drop

10. CATEGORIES OF
BLOOD STAINS
PASSIVE
TRANSFER
PROJECTED

11. PASSIVE
DEFINITION: drops created or formed by the force of gravity acting alone.

12. EXAMPLES:
Drops
Drip Patterns
Pools
Clots

13. PICTURES:

14. TRANSFER
DEFINITION: created when a wet, bloody surface comes in contact with a secondary surface.

15. EXAMPLES:
Contact bleeding
Swipe or Smear
Wipe
Smudge

16. PICTURES:
A recognizable image of all or a portion of the original surface may be observed in the pattern.

17. PROJECTED
DEFINITION: created when an exposed blood source is subjected to an action or force, greater than the force of gravity.

18. EXAMPLES:
Arterial Spurt / Gush
Cast-Off
Impact Spatter

19. PICTURES:

20. Low Velocity Medium Velocity High Velocity
cATEGORIES OF
IMPACT SPATTER
Low Velocity
Medium Velocity
High Velocity

21. LOW VELOCITY Gravitational pull up to 5 feet/sec.
Relatively large stains 4mm in size and greater.
Gravitational pull up to 5 feet/sec.

22. MEDIUM VELOCITY Force of 5 to 25 feet/sec.
                                                       
Preponderant stain size 1 to 4mm in size.
Force of 5 to 25 feet/sec.

23. HIGH VELOCITY Force of 100 feet/sec. or greater.
Preponderant stain size 1mm or greater.
Force of 100 feet/sec. or greater.

24. DIRECTIONALITY
OF BLOOD
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.

25. When a droplet of blood strikes a surface perpendicular
(90 degrees) the resulting bloodstain will be circular. That being the length and width of the stain will be equal.
90○ ANGLE

26. Blood that strikes a surface at an angle less than 90 degrees will be elongated or have a tear drop shape.
70○ ANGLE

27. 45○ ANGLE
10○ ANGLE
30○ ANGLE
5○ ANGLE

28. ANGLE
OF IMPACT
ANGLE of IMPACT is the acute angle formed between the direction of the blood drop and the plane of the surface it strikes.

30. By utilizing trigonometric functions, it’s possible to determine the impact angle for any given blood droplet.

31. By accurately measuring the length and width of a bloodstain, the impact angle can be calculated using the SIN formula below:
AOI = SIN-1 W / L

32. EXAMPLE
Finding AOI
LENGTH = 5.9cm
WIDTH = 2.6cm

33. SOLUTION: AOI = SIN-1 W / L AOI = SIN-1 2.6/5.9 AOI = SIN-1 (.44)

34. POINT OF
CONVERGENCE
DEFINITION: The common point, on a 2 dimensional surface, over which the directionality of several bloodstains can be retraced.

35. possible to determine a 2D point (or area)
Once the directionality of a group of stains (one or two stains is not sufficient) has been determined, it's
possible to determine a 2D point (or area)
for the group of stains.

36. By drawing a line through the long axis of a group of bloodstains, the point of convergence can be determined.
LONG AXIS / LENGTH

37. Point of Convergence (2D)

38. POINT OF ORIGIN
DEFINITION: lies at a point in space above the point of convergence. Measurement of the impact angle allows for translation of the 2-D image (convergence) into a 3-D one (origin).

39. TO DETERMINE WHERE THAT POINT IS LOCATED:
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.

40. FORMULA: PO = TAN (AOI) x y
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

41. Finding PO EXAMPLE GIVEN:
DISTANCE FROM BLOODSTAIN (to POC): 90cm AOI (calculated from AOI formula): 30°
SOLUTION:
PO = TAN (30°) x 90cm
PO = .577 x 90cm
= 52cm

42. Point of Origin
(3D --- use Z axis)

43. In practice (at a crime scene), strings, tapes and protractors are commonly used.

44. Computer programs can also be used.