Bloodstains can aid in the determination of the following:
� The distance between the target and impact site
� Point of origin(s) of bloodstains
� The angel at which a blood droplet struck a surface
� Type and direction of impact
� Speed with which blood left its source
� Movements during bloodshed
� Minimum numb
what important features to consider during bloodstain analysis?
1. surface texture
2. direction and angle
3. size
4. flow
5. shape
important Characteristics of liquid blood
1. Specific gravity
2. Viscosity
3. Surface Tension
Surface Tension
- is a characteristic of liquids whereby they are resistant to penetration or separation. The surface acts to reduce surface area. A small mass of liquid which becomes detached becomes rounded into a sphere; the shape gives the minimum service area for an
how does blood flow and fall?
- Blood flowing downwards towards the fingertips from a cut on the hand accumulates on the fingertip and increases in volume until the gravitational pull (its weight) exceeds surface tension. Such droplets will have a fairly uniform volume of 0.05 ml. Mor
how to know which direction of blood movement?
- blood that hit a surface from a non 90 angle will have elongated shape with the narrow pointed end showing the direction of movement
- 90 angle impact will just show a circular shape
what is the average volume of a blood droplet?
0.05 ml
what affects Terminal velocity of the falling blood drop?
1. size
2. medium it is falling through
1. Smaller drops - have a lower terminal velocity and acquire it after a shorter fall distance.
2. Larger droplets - accelerate over a greater distance and therefore attain a greater terminal velocity
Terminal velocity
the constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration.
does a small or large drop of blood have a bigger terminal velocity?
large drop of blood
what impacts that Size of the bloodstain more - target surface or distance fallen?
- depends on the nature of the target surface > distance fallen
why?
- The size of the resulting blood spot will vary only slightly with increasing fall distance and above a fall distance of seven feet there is little change in the diameter of the blood s
above a fall distance of ___________ feet there is little change in the diameter of the blood spot.
7
what affects the Shape of the blood spot the most?
- depends mostly on the texture of the target surface
ex.
1. Blood spots landing on SMOOTH glass will be consistent and uniform in shape (CIRCULAR)
2. mass blood spots landing on TEXTURED surfaces such as paper and wood will be of variable shape and will
angle of impact
- the acute angle formed between the path of a blood drop and the surface it contacts
how does an angled 90 degree impact affect bloodstain pattern?
Angled impact= vertical drop onto tilted target
- Blood striking a smooth surface at this angle results in an approximately circular blood stain and with NO tail or elontgation
how does an angled impact that is NOT 90 degrees affect bloodstain pattern?
- As the angle of impact becomes a more oblique (slanted) the blood stain becomes more elongated and its length to width ratio increases
how to mathematically determine Impact of Angle (A)
A = sin-1 (width of stain/ length of stain)
Effect of horizontal motion
- A blood spot striking a horizontal surface with a horizontal component to its motion will have a characteristic pattern due to a small drop being cast off from the far edge of the main droplet. This appearance is quite different to a drop falling vertic
Point of convergence
- Drawing lines along long axis of several stains will show a point of convergence at their origin.
Point of origin
- Lies at a point in space above the point of convergence.
- Measurement of impact angle allows translation of 2-D image (convergence) into 3-D (origin).
- At a crime scene, strings, tapes and protractors are commonly used. Computer programs are also util
what is the most common type of bloostain pattern found at a crime scene?
Impact Spatter
Impact Spatter
- Bloodstain pattern produced when an object makes forceful contact with a source of blood, projecting drops of blood outward from the source.
- the patterns consist of many drops in direct lines from the origin of blood to the stained surface
as the velocity of blood spatter increases what happens to the diameter of the blood drop? increases or decreases?
decreases
how are Blood spatter patterns are classified?
- according to the velocity with which the blood is struck
Low-velocity blood spatter:
velocity of blood at impact: less than 5 ft per second
examples:
1. free-falling blood under the influence of gravity
2. blood cast off from fist, shoe, weapon, dripping, splashing
Blood spot diameter: 4 mm or greater
Medium velocity blood spatter
velocity of blood at impact: 5 to 25 ft/s
Examples: blows with a baseball bat, hammer, axe or similar instrument
Blood spot diameter: 1 to 4 mm
High velocity blood spatter:
velocity of blood at impact: 100 ft/s or greater
Examples: gunshot; high velocity machinery; explosion
Blood spot diameter: less than 1 mm (a fine mist)
Back spatter
- results from blood being blown back from gunshot entry wound towards the firer and weapon
- blood projected backwards from source
Forward spatter
- results when blood exits the wound and passes in the same direction as the projectile (bullet) (away from the shooter)
- blood moves out and away from source
Projected blood spatter:
- Blood projected at velocity exceeding that of gravity often results in a spatter pattern wave with irregular spiny edges around the central bloodstain. Running or stepping into a pool of blood is typical of this pattern.
cast-off blood spatter
- bloodstain pattern that is created when blood is flung from a blood covered object in motion onto a surface
- Such staining is often apparent on the walls and ceiling in indoor situations. The direction and origin of the backswing is often clearly disce
Dripped blood:
- When blood drips into itself, many small droplets are projected upwards into the air and impact around the central irregular blood pool at in the right angles and obliquely, resulting in surrounding circular and oval blood spatter patterns.
Splashed blood
- Blood volumes exceeding 1 ml, traveling at a velocity of less than 5 ft per second or subjected to a minor impact, squirted, thrown against a vertical surface, or stomped.
- Results in an irregular central splashing pattern, surrounded by directional el
Arterial spurting
- Characteristic bloodstain pattern containing spurts due to blood exiting under pressure from an arterial injury.
- Wave form and associated flow patterns may be evident because of the spurting and large volume of blood associated with this type of injur
swipe patterns:
- Object moves through a wet bloodstain. Feathered edge suggests directionality
Transfer patterns:
- Wet, bloodied object contacts a secondary surface
- Transfer from hand, fingers, shoes, weapon, and hair.
- Transfer to walls, ceilings, clothing, and bedding.
- Produces mirror-image of bloodied object
Flow pattern:
- bloodstain patterns made by drops or large amounts of blood moving due to the pull of gravity
- Blood flows horizontally & vertically, altered by contours, obstacles; often ends in a pool. Pooled blood on absorbent surfaces may be absorbed and diffused
Void patterns:
- "An area within a deposited spatter pattern that is clear of spatter, caused by an object or person blocking the area at the time of the spatter's deposition