1. Blood & Bloodstain Pattern Analysis-Review

2. Nature of Blood
The word blood refers to a highly complex mixture of cells, enzymes, proteins, and inorganic substances.
Plasma, which is the fluid portion of blood, is composed principally of water.
Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets are the solid materials suspended in plasma.
Antigens, usually proteins, are located on the surface of red blood cells and are responsible for blood-type characteristics.

3. Blood Typing
More than 15 blood antigen systems have been identified, but the A-B-O and Rh systems are the most important.
An individual that is type A has A antigens on his/her red blood cells, type B has B antigens, AB has both A and B antigens, and type O has neither A nor B antigens.
Rh factor is determined by the presence of another antigen, the D antigen.
People having the D antigen are Rh positive; those not having the antigen are Rh negative.
For every antigen there is a specific antibody that will react with it to form clumps known as agglutination.
Thus, if serum containing anti-B is added to red blood cells carrying B antigen, they will immediately react.

4. Ratios of Blood Types O+ 1 in 3 persons O- 1 in 15 persons
A+ 1 in 3 persons
A- 1 in 16 persons
B+ 1 in 12 persons
B- 1 in 67 persons
AB+ 1 in 29 persons
AB- 1 in 167 persons

5. Forensics of Blood
The criminalist must be prepared to answer the following questions when examining dried blood:
(1) Is it blood?
(2) From what species did the blood originate?
(3) If the blood is of human origin, how closely can it be associated to a particular individual?
The determination of blood is best made by means of a preliminary color test.

6. The Tests For the Presence of Blood.
A positive result from the Kastle-Meyer color test is highly indicative of blood.
Hemoglobin causes a deep pink color.
Alternatively, the luminol test is used to search out trace amounts of blood located at crime scenes.
Produces light (luminescence) in a darkened area.
Microcrystalline tests, such as the Takayama and Teichmann tests, depend on the addition of specific chemicals to the blood so that characteristic crystals will be formed.
Precipitin test
Gel Diffusion

7. Wet blood has more value than dried blood because more tests can be run.
For example, alcohol and drug content can be determined from wet blood only. Blood begins to dry after 3-5 minutes of exposure to air. As it dries, it changes color towards brown and black.
Blood at the crime scene can be in the form of pools, drops, smears, or crusts.
Pools of blood obviously have more evidentiary value in obtaining a wet sample.
Drops of blood tell the height and angle from which the blood fell. The forensic science of blood spatter analysis says that blood which fell perpendicular to the floor from a distance of 0-2 feet would make a circular drop with slightly frayed edges.
Drops from a higher distance would have more pronounced tendrils fraying off the edges (a sunburst pattern).
A blood smear on the wall or floor tells the direction of force of the blow. 
The direction of force is always in the direction towards the tail, or smaller end, of the smear, or splatter. In other words, the largest area of the smear is the point of origin (a wave cast-off pattern).
Blood crusts need to be tested with crystalline methods to make sure it's blood.

8. Refrigerated red blood cells have a shelf life of about 42 days, and the serum containing white blood cells can be refrigerated much longer, almost up to a year.  DNA can be extracted from blood (if white blood cells which always contain a nucleus are present), and also from sperm, bone marrow, tooth pulp, and hair roots.
Blood, however, is commonly used in DNA testing, as per the following steps:
Blood samples are collected from the victim, defendant, and crime scene
White blood cells are separated from red blood cells
DNA is extracted from the nuclei of white blood cells
A restrictive enzyme is used to cut fragments of the DNA strand
DNA fragments are put into a bed of gel with electrodes at either end
Electric current sorts DNA fragments by length
An absorbent blotter soaks up the imprint; it is radioactively treated, and an X-ray photograph (called an autoradiograph) is produced 

9. Blood Spatter (or splatter)
Blood drops form different shapes and sizes
Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

10. Blood drops fall as small spheres
Blood Spatter > Distance
Determining Distance Blood Falls
Blood drops fall as small spheres

11. Determining Distance Blood Falls
Blood Spatter > Distance
Determining Distance Blood Falls
Drops form circle when hitting surface
Size depends on speed of blood drop

12. Determining Distance Blood Falls
Blood Spatter > Distance
Determining Distance Blood Falls
Faster drop = larger diameter (size)
Higher distance = larger diameter
Due to air resistance, speed maxes out at distances above about 7 feet

13. Determining Distance Blood Falls
Blood Spatter > Distance
Determining Distance Blood Falls
However, size of drop also depends on the volume of the drop.
Volume depends on the object blood originated from (needle = small; bat = large).

14. The distance a drop has fallen cannot be measured.
Blood Spatter > Distance
Determining Distance Blood Falls
Since the volume of blood is unknown…
The distance a drop has fallen cannot be measured.

15. Effect of Surface Smooth surface = smooth sphere
Blood Spatter
Effect of Surface
Smooth surface = smooth sphere
Rough surface may cause some splatter

16. Determining Direction of Blood
Blood Spatter > Direction
Determining Direction of Blood
Narrow end of a blood drop will point in the direction of travel.

17. Determining Direction of Blood
Blood Spatter > Direction
Determining Direction of Blood
If more than one drop (from spatter) results, the point of origin can be determined

18. How do we Determine the point of origin of Blood?
Blood Spatter > Direction
How do we Determine the point of origin of Blood?
If more than one drop (from spatter) results, the point of origin can be determined

19. Determining Direction of Blood
Blood Spatter > Direction
Determining Direction of Blood
This is a 2-dimensional point of origin.
It is possible to determine the 3-D point of origin

20. How Do We Determine Direction of Blood?
Blood Spatter > Direction
How Do We Determine Direction of Blood?
The angle can be determined mathematically.
Width/Length, then take the inverse sin (sin-1).
This number is the impact angle (90 = perpendicular to surface; <10 at a sharp angle)

21. Blood Spatter > Direction
For each blood drop, a string can be guided back to the point of origin.

22. Blood Spatter
Types of Spatter
Spattered Blood = random distribution of bloodstains that vary in size
Amount of blood and amount of force affect the size of blood spatter.
Can result from gunshot, stabbing, beating

23. Blood Spatter
Spattered Blood can:
Help determine the location of the origin of the blood source.
Help determine the mechanism which created the pattern.

24. Blood Spatter
Spattered Blood
In general, for higher impacts, the pattern is more spread out and the individual stains are smaller.
Low impact = beating
High impact = gunshot

25. Blood Spatter
Types of Spatter
Gunshot Spatter = can result in a mist-like spatter that indicates a gunshot.
Not all gunshots will result in misting.
If misting is present, it is most likely a gunshot.

26. Blood Spatter
Gunshot Spatter
Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits).

27. Blood Spatter
Types of Spatter
Beating and Stabbing Spatter = larger individual stains
First blow usually doesn’t result in spatter since there is not yet any exposed blood.

28. Blood Spatter
Types of Spatter
Satellite Spatter = free falling drops of blood that fall onto a spatter pattern.
These drips are usually much larger than impact spatter.
However, blood dripping into blood can create a spatter.

29. Types of Spatter Castoff Pattern = Blood flung off of swinging object.
Blood Spatter
Types of Spatter
Castoff Pattern = Blood flung off of swinging object.
Can reconstruct where assailant and victim were positioned.

30. Blood Spatter
Types of Spatter
Expirated Bloodstain Pattern = Blood can accumulate in lungs, sinuses, and airway. Forcibly exhaled.
Can appear like beating or gunshot pattern.
May be mixed with saliva or nasal secretions.

31. Alteration of bloodstain over time
Blood Spatter
Alteration of bloodstain over time
Blood dries and clots over time.
Difficult to estimate the time the blood exited the body.
Clotted smears can indicate time of movement.

32. Categories of Blood Stains
Passive
Transfer
Projected

33. Transfer Bloodstains
A transfer bloodstain is created when a wet, bloody surface comes in contact with a secondary surface.
A recognizable image of all or a portion of the original surface may be observed in the pattern, as in the case of a bloody hand or footwear.

34. Passive Bloodstains
Passive bloodstains are drops created or formed by the force of gravity acting alone.

35. Projected Bloodstains
Projected bloodstains are created when an exposed blood source is subjected to an action or force, greater than the force of gravity. (Internally or Externally produced)
The size, shape, and number of resulting stains will depend, primarily, on the amount of force utilized to strike the blood source.

36. Projected Bloodstains
Arterial Spurt/Gush
Bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery
Cast-off Stains
Blood released or thrown from a blood-bearing object in motion
Impact Spatter
Blood stain patterns created when a blood source receives a blow or force resulting in the random dispersion of smaller drops of blood.
Velocity affects stain pattern

37. Impacted Spatter
Low Velocity
Medium Velocity
High velocity—greater than 25 feet per second, usually feet per second; gives a fine mist appearance
Medium velocity—5 to 25 feet per second
Low velocity—5 feet per second or less
High Velocity