Forensic SerologyForensic Science

Composition of Blood• Blood is a complex mixture of cells, enzymes,

proteins, and inorganic substances

• Main Components:

– Erythrocytes = red blood cells (RBCs)

– Leukocytes = white blood cells (WBCs)

– Platelets = clotting factors

– Plasma = the liquid part

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Antigens and Antibodies

3

• Antigens: proteins on surface of cells (including RBCs) that identify them

– Different types of cells have different antigens

• Antibodies: Y-shaped immune system proteins that recognize and bind to foreign objects to neutralize them

– You get vaccines to develop these!

• Agglutination: clumping of antibodies when they bind to their specific antigen

ABO Blood System

• Anti-A antibodies will agglutinate (clump) in Type A blood

• Anti-B antibodies will agglutinate in Type B blood

• Type AB blood will agglutinate in anti-A or anti-B serum

• Type O blood will not cause agglutination4

Blood Type Antigens on RBCsAntibodies in Blood Serum

A A anti-B

B B anti-A

AB A and B none

O none anti-A and anti-B

Blood Donors and Recipients

BLOOD TYPE DONATES TO RECEIVES FROM

A A, AB A, O

B B, AB B, O

AB AB A, B, AB, O

O A, B, AB, O O

• Type AB blood is the universal recipient because it can take any of the 4 types and not agglutinate

• Type O (most common) is the universal donor it does not have any antigens to cause agglutination

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Rh Factor

• Rh (Rhesus) factor is another important blood antigen

• This is the positive (+) and negative (-) of blood types

– Rh- means you don’t have the antigen

• Rh factor affects blood donation compatibility

– Rh+ blood types can accept either Rh+ or Rh-

– Rh- can only accept Rh- blood or it will agglutinate 6

Genetics of Blood• Blood types are determined by looking at 2

inherited genes (one from each parent)

• There are 3 common alleles for blood types: A, B, and O, with 6 possible combinations

BLOOD TYPE ALLELE COMBINATIONS

A AA, AO

B BB, BO

AB AB

O OO7

Punnett Square

Biological Properties of Blood

• Blood delivers nutrients and oxygen to the cells and transports waste products away from cells.

• Red blood cells

carry oxygen

and carbon

dioxide.

Biological Properties of Blood

• White blood cells fight off infection and reject foreign tissue.

Biological Properties of Blood

• Platelets assist in clotting.

Blood Stain AnalysisForensic Science

Testing for Blood

When they find a red stain, investigators must ask themselves 3 questions:

1. Is it blood?

2. Is it human blood?

3. Whose blood is it?

Presumptive tests (color tests) indicate the presence of blood

• Kastle-Meyer: this solution of phenolphthalein turns bright pinkwhen it encounters the blood protein hemoglobin

– Some vegetable matter like potatoes and horseradish can give a positive K-M result, but… you’re probably not going to find those at a crime scene

Is it blood?

Is it blood?

• Luminol: When sprayed on blood, this solution produces a faint blue light

– This can work on blood that someone tried to clean up

Is it human or animal blood?

Precipitin Test

• Serum made in rabbit contains antibodies against human blood

• Crime scene blood is layered on top of the anti-human serum in a test tube

• If the sample is positive for human blood, a cloudy precipitate will form where the 2 layers meet

Whose blood is it?

• A DNA analysis would have to be performed to find out exactly who the blood belongs to

– But ABO blood typing can narrow down a pool of suspects.

Blood Spatter Analysis

Impact Spatter:

Transfer

Occurs when an

object impacts a

source of blood

Passive Dripping

Blood Stain Evidence

• Bloodstain patterns can help investigators reconstruct events in a crime scene.

• Analysis of the blood stain can tell whether it is animal or human.

• Projected blood stains are called blood spatter.

Blood Spatter• Blood spatter analysis can approximate:

– distance from the source of the blood to the pattern– direction from which the blood impacted– speed the droplet was traveling– location of the point of origin– movement of a bleeding individual throughout the

scene

• These approximations may agree or disagree with statements made by witnesses, victims, or suspects.

• This can help determine the manner of death

Physical Properties of Blood

• Unlike water, blood is a suspension of solids and gases in a liquid.

• Blood behaves differently than water when it is moving.

• The viscosity of blood lowers as its shear rate increases (pumps easier at high flow rates).

Physical Properties of Blood

• The surface tension of blood is slightly less than water.

• Blood forms a spherical projectile, not a teardrop.

• A large amount of blood from a small wound means that the victim survived for a fair length of time.

• Blood normally clots in 3-15 minutes.

Physical Properties of Blood

• Fluid flow is driven by a pressure difference.

• Blood pressure drops with excessive blood loss and the bleeding rate slows due to this lower pressure difference.

• Upon death blood pressure falls to zero and bleeding stops.

Blood Spatter Analysis - SurfaceWhen examining blood spatter, is it

important to consider the surface

• Hard and nonporous surfaces like glass and tile generally result in round drops with less spatter

• Rough surfaces like carpeting, wood, or fabric usually result in irregularly shaped stains with serrated edges and possibly satellite spatter– Satellite spatter are the tiny droplets that

break away from the main drop

Surface Tension

• Surface tension acts to reduce surface area. It resists penetration and separation.

• The smallest surface area to volume ratio is a sphere, which is why blood droplets fall in a spherical rather than teardrop shape.

• This sphere of blood does not break up until impact with a solid surface.

Drop Sizes

• The standard drop size is about 0.05 mL.

• Rapid bleeding gives a slightly larger drop.

• Shaking movement casts off smaller drops.

• Gunshot wounds produce high velocity spatter that results in a spray of very tiny drops.

Blood Spatter Analysis - Speed– Small droplets (less than 1 mm; spray) mean

high velocity around 100 ft/s

• Example: gunshot wound

– Medium droplets (1-4 mm) mean medium velocity around 25 ft/s

• Example: stabbing

– Large droplets (4-6 mm) mean low velocity around 5 ft/s

• Example: blunt object impact such as a hammer to the head

Free Falling Blood Droplets

• Blood droplet size affects both the terminal velocity and the distance that the droplet will fall before reaching terminal velocity.

Droplet A B C D

Volume (µL) 0.06 0.12 0.50 50

Diameter (mm) 1.10 1.32 2.12 4.60

Terminal Velocity (m/s) 2.2 3.3 4.6 7.5

Distance (m) 0.6 0.9 2.5 5

Free Falling Blood Droplets

A smooth surface will cause the spatter to spread out smoothly.

An irregular surface will create a broken edge and more small spatter.

Wave Cast-Off

• When a droplet bounces off a surface the tails of the parent and wave cast-off will point toward each other.

Blood Spatter Analysis - Height

• How far from the ground a blood drop originated is reflected in the size of the blood drop.

• A drop from farther up will spread out more upon impact.

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Blood Spatter Analysis - Direction

• Momentum tends to keep blood moving the direction it was traveling

– In an elongated blood drop, the tail points in the direction of the blood’s movement

– Satellite droplets appear in front of the moving droplet of blood

direction of movement

Determining Directionality

• The impact angle can be determined by measuring the degree of elliptical distortion.

• At right angles the blood drop is circular.

Blood Spatter Analysis - Angle

• The angle of impact can be found mathematically

• Divide the width (shorter side) of the blood drop by the length (longest part)

• Then take the inverse sin, also called “arcsin” or “sin-1”of that number to get the angle.

angle = arcsin (width/length)

Blood Spatter Analysis - Angle

• The smaller the angle (meaning the source was closer to the floor) the longer and more stretched the blood drop looks

Angle of Impact

The bottom of the

spatter stain will be

more dense than the

top of the stain.

Trigonometry and Angle of Impact

• To determine the angle of impact:

– Measure the width and length of the blood spatter. Length must be longer than width.

– Divide width by length.

– Take the arcsine of your result.

– This formula will not produce accurate results at extreme angles ( less than 10˚ or greater than 60˚).

𝑠𝑖𝑛𝜃 =𝑤

𝑙𝜃 = arcsine

𝑤

𝑙

Blood Spatter Analysis - Convergence

• You can figure out where blood came from by drawing lines through the long axis of the droplet.

• Remember the tail (and satellites) indicate the direction blood was moving, so the origin is the opposite direction.

• Where lines meet is called the area of convergence.

area of convergence

Area of Convergence (2d area)

• To determine the area of convergence, investigators calculate the direction and angle of many blood stains.

• For each blood stain analyzed, they place a string at the stain which is parallel to the angle of the blood droplet.

Area of Convergence (2d area)

• After many strings have been placed, a general area of convergence will appear where the strings overlap.

• This can also be done on a computer with image analysis software.

Blood Spatter Analysis - Origin

• You can use string to help you recreate point of origin

• There are also computer programs to help

– “No More Strings”

DEXTER

Blood Spatter Analysis – Origin

• Lines of convergence give you a direction that blood came from, but not height.

• You can use the angle of impact and trigonometry to determine how far up the blood came from

Add this formula to your notes…

To find the height of the origin of blood spatter…

height = tanθ x distance to convergence

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• Remember SOH CAH TOA

– Tangent is opposite/adjacent

tanθ = height/distance to convergence

so height = tanθ x distance

height = tan27° x 5.75 ft

height = 0.5095 x 5.75 ft

height = ~2.9 ft above the ground

angle

opposite

adjacent

Yay math!

Blood Spatter Analysis - Origin

• Use angle of impact and convergence lines to make an imaginary right triangle

• You know the angle of impact, you know the “adjacent” side length

• Solve for height using the Law of Tangents

Point of Origin (3d volume)

• The procedure for generating the point of origin is just like the area of convergence, except the angle of impact for each stain is calculated.

• This is a method of adding a third dimension to the 2d area of convergence calculation.

2d Solution – no angular data

Point of Origin (3d volume)

• The procedure for generating the point of origin is just like the area of convergence, except the angle of impact for each stain is calculated.

• This is a method of adding a third dimension to the 2d area of convergence calculation.

3d Solution – with angular data

Point of Origin (3d volume)

• The term point of origin is really a misnomer, as the 3d intersection of the strings creates a 3d volume rather than a single point.

• This can also be done with a computer by taking careful measurements at the scene for each blood droplet’s dimensions, location, and direction.

Limitations of our Model

• Projectiles launched at an angle do not follow a straight line.

• In our previous example of calculating the point of origin, it would be lower than calculated because the blood would follow an arc rather than a line. This simplified model doesn’t account for gravity.

Limitations of our Model

• At high velocities (gun shots) the linear model of projectile motion is fairly accurate.

• The model is better suited to disproving testimony than to accurately re-constructing the events at a crime scene.

• In a real crime scene, the investigator usually uses lasers instead of string to allow others access to the crime scene.

Blood Analysis – Wrap Up

• Ask:

– Is it blood?

– Is it human blood?

– Whose blood is it?

• Figure out:

– Speed of impact

– Angle of impact

– Area of convergence

– Point of origin

CLASS CHARACTERISTICS:

•species

•blood type

•Rh factor

•diseases?

INDIVIDUAL CHARACTERISTICS

•DNA profile

Forensic Serology:Other Body Fluids

Other Body Fluids: Saliva

• Consists of water, mucin for lubrication, amylase enzyme for digestion, buccal (cheek) cells that could provide DNA

• Saliva is often associated with sexual assaults and bite mark evidence

• Presumptive tests for saliva check for the amylase enzyme

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Other Body Fluids: Semen

• Consists of water, spermatozoa, enzymes, salts

• Semen is often evidence in sexual assault cases

• Presumptive tests for semen include

– Black light fluorescence

– Chemical test for acid phosphatase (enzyme from prostate), turns purple when present

• Confirmatory tests include microscopic examination for presence of sperm

• DNA analysis can individualize the sample55

Other Body Fluids: Urine

• Urine is composed mostly of water, and also includes urea (nitrogenous compound) and salts.

• Urine is most often used for the detection of drugs in the body

• EMIT (Enzyme-Multiplied Immunoassay Technique) test reveals the presence of specific drugs through antibody binding

• 0135158494, Saferstein, Richard. Forensic Science: An

Introduction. New Jersey: Pearson Prentice Hall, 2011.

• 0536522820, Saferstein, Richard. Criminalistics: An

Introduction to Forensic Science. 8th ed. Upper Saddle

River, NJ; Pearson Prentice Hall, 2004.

• Sam Sheppard by Fred McGunagle

http://www.trutv.com/library/crime/notorious_murders/fam

ous/sheppard/index_1.html

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