Blood: Forensic Uses of Blood at a Crime Scene

Blood properties Blood types

Bloodstain Pattern Analysis

What is Blood?• Fluid circulating throughout the body• Transports oxygen, electrolytes, nourishment, hormones, vitamins and antibodies to tissues and transports cellular waste to excretory organs• Components of blood:

• Plasma-55% of the blood (straw-colored liquid in which the blood cells are suspended)

• Red blood cells (anucleated – carry O2 and CO2)

• White blood cells (nucleated – defense against infection and disease)

• Platelets (cell fragments responsible for clotting)

What is Blood?• On average, blood accounts for 7% of total body weight (about 10 pints)

• 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).

•In 1901, Dr. Landsteiner recognized that all human blood was not the same and he worked out the ABO classification system.•In 1940 he discovered the rhesus factor (Rh) in blood.

Microscopic Views

Bird Blood

Cat Blood

Dog Blood

Fish Blood

Frog Blood

Snake BloodHuman Blood

Horse Blood

Blood Disorders: hemophilia and sickle cell disease

Normal Human blood on left, human blood with sickle cell anemia on right

Blood Types There are 4 major groups based on the presence

of, and type of surface cell proteins: AB: have both A and B blood proteins and produce no

antibodies A: have only A proteins and produces antibodies to B B: Have only B proteins and produces antibodies to A O: have no blood proteins can produce antibodies to

both A and B

There are also surface cell proteins called Rh factors Individuals either have these (Rh+) or lack them (Rh-)

Blood Types: Codominance and Multiple Alleles

In blood types, there are three forms that your genes can come in – they can contain information for making the A protein, or the B protein, or neither protein

Let I = a gene, and a superscript for the form that gene comes in:IA = the A proteinIB = the B proteini = no protein

Genes You must have 2 copies of each gene, and the

combinations will determine the proteins you make, and therefore your blood type:

One final point, the A and B alleles are codominant (one is not dominant over the other), but both are dominant over the i gene

IAIA or IAi = blood type A IBIB or IBi = blood type B IAIB = blood type AB ii = blood type O Set-up a Punnett Square to determine blood type

of offspring…

The Underlying Genetic Bases of Blood Types

A blood will agglutinate in anti-A serum because it carries B antibodies. B blood will agglutinate in anti-B serum because it carries A antibodies.

Recall that blood types are determined by proteins found on the surface of red blood cells

Proteins are made by information in your DNA (genes)

Recall that you have 2 copies of each gene, and their make-up will determine what kind of protein you make

Blood type is determined, in part, by the ABO blood group antigens present on red blood cells

Blood Types - Testing

Probabilities

41% of US citizens has type A blood10% have type B blood4% have type AB blood45% have type O blood85% have Rh+ blood

So what is the probability of having B- blood?10/100 x 15/100 = 150/10,000 or 1 in 67

(so mathematically, Weber is not 1 in a million; only 1 in 67 based on blood type )

Forensic Use of Blood Types Serology is used to describe a broad scope of

laboratory tests that use specific antigen and serum antibody reactions.

Although DNA analysis has replaced most conventional serology tests, there is still some useful information in the blood

About 80% of the population are secretors Secretors secrete their blood antigens into their tears,

sweat, semen and saliva The presence of any of these substances permits

identification of the blood type of the suspect Knowing the blood type allows you to rule out

suspects (called exclusionary evidence) rather than identify them. Why?

Blood as individual evidence???

• Blood typing can be applied to a host of enzymes and proteins that perform specific functions in the body. Their presence or absence varies within the population. More than 150 serum proteins and 250 cellular enzymes have been isolated.

• Therefore, it is possible to use blood typing as individual evidence; however, it is not practical to achieve the statistics required because of the time and techniques involved. Also, most factors degrade with time.

• ABO/Rh typing, and often another kind of typing called MNS, are used as exclusionary tests in forensic science and paternity testing.

Problem to try…

The typical population in the United States shows and MNS distribution of M=30%, N=27%, S=48%.

If a blood stain found at the scene of a crime is found to be AB, N, Rh-, what are the chances that a suspect would have this combination of antigens? Is this good enough to convince a jury?

Criminalists must be prepared to answer the following questions when examining dried blood:

Is it blood?Determination of blood is best made by a

preliminary color test (mostly due to a catalytic decomp of peroxides by hemoglobin)

Hemastix strips or Hematest tablets: turns blueKastle-Meyer: turns bright pinkLuminol: produces light in a darkened area

What is the species of origin?Preciptin test determines animal or human blood

If it is human, how close can it be associated with a particular individual?

Caution – Gives False Positives!

The Kastle-Meyer test detects the presence of enzymes in the blood

Other substances such as potatoes and horseradish contain the enzyme peroxidase which will also react with phenolpthalien

Thus, a positive Kastle-Meyer test is not definitive, and only indicates the possible presence of blood

Other tests like precipitin are needed to verify the presumptive results

Luminol Works in a similar fashion to phenolphthalein – except

detecting chemiluminescence instead of pink color. The chief catalyst (esp. in old blood samples) is iron, not

catalase False positives are possible: Cu, Fe, Co, bleach, plaster

walls Can test large areas at once Does not degrade DNA or blood antigens

Luminol

Blood Spatter AnalysisMost evidence at a crime scene such as

hairs, footwear, fingerprints and DNA is interpreted to determine the identity of the individuals involved

In contrast, bloodstain pattern analysis is used to determine what happened at a crime scene, and the sequences of events that took place

Blood Spatter

Blood drops form different shapes and sizesBlood spatter analysis uses the shapes

and sizes to reconstruct the crime scene.

Blood – a Liquid

To a blood spatter analyst, blood is nothing more than a liquid

As such, it behaves in predictable ways (fluid dynamics)

The features that blood has that many other liquids don’t are:Permanence: when blood dries, it leaves a

visible residueColor

Direction, Volume and Surface Texture Affect Blood Patterns

Directionality: relating to or indicating the direction a drop of blood has traveled from its point of origin

Spot size and shape: vary according to the amount of blood, the manner in which it is propelled from a source and the surface texture the blood drop lands on

In general, the harder and less porous a surface, the less spatter results.

Blood Spatter

Blood drops fall as small spheres – not as tear drops – due to its surface tension & cohesion

The smaller the drop, the more spherical it will be

Under normal conditions, blood will form drops of uniform size – roughly 0.05 ml and 6 mm in diameter

Surface and Blood Spatter The type of surface the blood strikes affects

the amount of resulting spatter, including  the size and appearance of the blood drops.

Blood droplets that strike a hard smooth surface, like a piece of glass, will have little or no distortion around the edge.

Blood droplets that strike linoleum flooring take on a slightly different appearance. There may be distortion (scalloping) around the edge of the blood droplets.

Surfaces such as wood or concrete are distorted to a larger extent.   Notice the spines and secondary spatter present.

Height/Surface

Single drop of blood falling from various heights (m) onto various surfaces

smooth floor paper towel fabric

0.5

1

2

3

0.5

1

2

3

Blood Spatter – Size of Drop

Determining Distance Blood Falls

Drops form circle when hitting surfaceSize depends on speed of blood drop

Blood Spatter

Determining Distance Blood FallsFaster drop = larger diameter (size)Higher distance = larger diameter

Due to air resistance, speed maxes out at distances above about 7 feet

Blood Spatter

Determining Distance Blood FallsHowever, size of drop also depends on the

volume of the drop.

Volume depends on object blood originated from (needle = small; bat = large)

Blood Spatter

Since the volume of blood in a drop is generally unknown…

It is not possible to establish with a high degree of accuracy the distance that a passive blood drop has fallen

So, what can we tell from bloodstains?

Blood Spatter – Horizontal Motion

Determining Direction of Blood

When a drop hits at an angle other than 90º, it will form a tear drop shape on the surface it hits

Narrow end of a blood drop will point in the direction of travel.

Remember that a drop at 90º leaves a spherical drop The steeper the angle, the longer and narrower the drop is

tail points in direction of

travel

one exception!

Direction of Blood

Blood Spatter

Determining 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)

Blood Spatter

Determining Direction of Blood

If more than one drop (from spatter) results, the point of origin can be determined

Blood Spatter

Determining Direction of Blood

This is a 2-dimensional point of origin. It is possible to determine the 3-D point of origin

Blood Spatter

For each blood drop, a string can be guided back to the point of origin.

Types of Spatter Passive spatter: Passive bloodstains are drops

created or formed by the force of gravity acting alone (ex: blood dripping off of a knife)

Projected spatter: 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) Forward spatter from an exit wound; back spatter from

an entrance wound. Spattered blood can:

Help determine the location of the origin of the blood source.

Help determine the mechanism which created the pattern.

Passive spatter and transfer patterns

Types of spatter cont.

Projected: types of patternsArterial gush-pattern shows large spurted stains

for each time that the heart pumps. Arterial blood is bright red, while veinous blood is dark red (oxygenated vs. deoxygenated)

Cast-off-created when a blood-covered object flings blood in an arc onto a nearby surface

Low velocity (cast off spatter)Medium velocity (cast off spatter)High velocity spatter (gunshots)

Types of Projected Blood 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 In general, for higher impacts, the pattern is

more spread out and the individual stains are smaller. Medium impact = beating High impact = gunshot

Projected – Arterial Spray

Arterial Spurt / Gush: Bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery

Large volume projected from arterial pressure

Projected –Cast-off

Usually found on ceilings – formed by the upstroke of a weapon containing blood (bat, crowbar etc)

Number indicates number of blows, plus one When found on a horizontal surface, suggests

sideways motion. Blood is deposited horizontally by the “backswings”

Cast off blood is usually traveling slowly – less than 5 ft per second Consequently the drops are typically smaller than

passive spatter (13-22 mm) – usually about 6mm (¼”) or less

Projected-Low Velocity

Deposited at less than 5 feet per second

Usually about 4mm in diameter

Usually is from a source that is dripping blood

Projected – Medium Velocity A bloodstain pattern caused by a

medium velocity impact or force to a blood source.

These type of spatters are normally smaller than those from low-velocity droplets (1-4 mm or less) and tend to come from impacts with blunt or sharp objects which distribute blood in all directions from the source of impact.

These can help determine the point of origin.

Blood is typically traveling between 5 -25 feet per second

Projected – High Velocity High velocity blood spatter occurs

when a strong, explosive force projects blood in a aerosolized spray Usually produced by a gunshot

These patterns produce very small droplets

The blood is in a mist, and as such, does not have much horizontal movement (less than 5ft) Blood is traveling 100 ft/sec or more Blood spatter is typically <1 mm

Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits)

Moral of the Story

Calculation using “straight-line” trajectory (no gravity and no air resistance) predicts a “launch” point higher than actual point. Calculations that don’t account for gravity and

air resistance usually give you a result that is twice that of the actual height – so you can correct (roughly by dividing your calculations by 2

More accuracy requires a better model and more specialized work.

Blood impression on pants, spatter on a wall, high velocity droplet and a flake of dried blood taken off of fabric