1) Origin(s) of bloodstain2) Distance of bloodstain from target3) Direction from which blood impacted

4) Speed with which blood left its source5) Position of victim & assailant6) Movement of victim & assailant7) 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.

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.

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.

“Fitting” of an ellipse in blood drop

Tail or spine

Parent Drop

• PASSIVE• TRANSFER• PROJECTED

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

EXAMPLES:

DropsDrip Patterns

PoolsClots

PICTURES:

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

EXAMPLES:

Contact bleeding Swipe or Smear

Wipe Smudge

PICTURES:

A recognizable image of 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 / GushCast-Off

Impact Spatter

PICTURES:

Low Velocity

Medium Velocity

High Velocity

LOW VELOCITY

Relatively large stains 4mm in size and greater.

Gravitational pull up to 5 feet/sec.

MEDIUM VELOCITY

                                                       

      

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

HIGH VELOCITY

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

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. That being 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

45○ ANGLE

30○ ANGLE

10○ ANGLE

5○ ANGLE

ANGLE of IMPACT is the acute angle formed between

the direction of the blood drop and the plane of the

surface it strikes.

By utilizing trigonometric 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 = SIN-1 W / L

LENGTH = 5.9cm

WIDTH = 2.6cm

Finding AOI

SOLUTION:

AOI = SIN-1 W / L

AOI = SIN-1 2.6/5.9

AOI = SIN-1 (.44)

AOI = 26.2°

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

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.

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 (2D)

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).

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.

TO DETERMINE WHERE THAT POINT IS LOCATED:

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): 90cm AOI (calculated from AOI formula): 30°

SOLUTION:

PO = TAN (30°) x 90cm

PO = .577 x 90cm

= 52cm

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

In practice (at a crime scene), strings, tapes

and protractors are commonly

used.

Computer programs can also be used.