Biological evidence - Blood

blood in crime

most frequently found body fluid in criminal investigations

bright red colour

comes from the heme molecule which binds to oxygen to facilitate transportation around the body

to increase ability to carry oxygen, RBC have no nucleus

why is DNA anlysis in blood depend on white blood cells

red blood cells have no nuclei to increase their capacity for carrying gases

nuclei is present in white proof cells

a minute drop of blood had enough white blood cells to yeild a DNA profile

two main objectives in analysing a bloodstain

to determine the source of the blood by comparing its DNA profile with reference samples from victims and suspects

to see if Blood stain analysis BPA will yield information about the incident

potential of blood as evidence

reconstruct the events which occurred during the crime

link the suspect to the bleeding victim

link the bleeding suspect to the victim or scene

link the victim or suspect or both to weapons, vehicles or other physical evidence

issues with blood as evidence

there are many circumstances in which blood does not transfer to assailant - if assailant left immediately after the injury which caused bleeding

is blood direct result of assault or secondary to it?

a victim lying in a pool of blood may have started to bleed from head injury sustained from falling during the assault

blood transfers to other people or items

by direct contact or through drops that travel through the air, aerosols

the pattern of the stain BPA

may give information on where an assault started, how the victim moved furing the assault and what the victim did after the assault if he or she survived

patterns may indicate if more than one person bled at the scene

searching for blood at the scene

good light is vital when searching fo bloodstains at a scene

scenes of crime examiners need appropriate torches for searching purposes

bloodstains are not enhanced by fluorescent or regular white light

a presumptive test KM test for blood will indicate if the stain is blood or not

purpose of presumptive test / KM test for blood

to indicate if the stain is blood or not

presumptive tests for blood

colour test for blood on the properties of haemoglobin in blood

extremely sensitive and can easily detect very small quantities of blood

when negative the test often helps to eliminate stains that do not need to receive any further consideration

these tests may be recognised as those that produce a visible colour or result in the release of light

KM test - Kastle-Meyer Test

test based on the reaction where oxygen is liberated from hydrogen peroxide by the peroxidase activity of the heme group of haemoglobin in red blood cells

phenolphthalin → oxidised (heme) phenophathalin (colourless to pink)

limitation of KM test

not specific to blood

this activity is present in other biological and non biological samples such as plant peroxides, metallic salts and strong oxidising reagents

a pink colour is an indication of blood, not proof of blood

KM Kit procedure

using fresh filter paper, rub the surface of the stain to be tested

add one drop of absolute ethanol to the filter paper

add a drop of KM solution

add a drop of the hydrogen peroxide solution

if pink colour develops on the filter paper, it is an indication that blood is present

if no pink colour develops, it indicates that no blood is present

discard the filter paper

Luminol test

if it is suspected that a scene has been cleaned and little or no blood has been found, spraying with luminol could be considered

luminol reacts with haemoglobin in diluted blood to give a strong blue/green luminescence when viewed in the dark

luminol test drawbacks

not specific for blood and can react with other materials such as saliva, bleach and animal and vegetable proteins

scene must be thoroughly cleaned after its use and before its released back to its owners

other presumptive tests for blood

leucomalachite green

tetramethylbenzidine

leucomalachite green/ TMG presumptive test for blood

LMG testing works similarly to KM test but uses LMG reagent instead of phenolphthalein

the bloodstain will turn green when exposed to the reagent

Tetramethlybenzidine presumptive test for blood

turns blue in the presence of blood

immediate reaction

name of lab test for blood origin

precipitin test

determines if blood is of human origin

precipitin test

determines if blood is human origin

uses antibodies against human blood proteins to form a precipitate

an extract of the blood stain is layered on top of a layer of the antibody solution in a capillary tube

formation of a band or cloudy ring at interface

methods of taking bloodstains at scenes

scraping

tape lifting

swabbing

cutting method

scrapping method

bloodstains can be scraped into a piece of paper which is then folded and placed in an envelope

tape lifting method

stain is covered with a strip of sellotape

stain is broken up by pressing on the tape to improve adhesion

sellotape can be plated onto a sheet of cobex/acetate and packed in an envelope or a plastic bag

not recommended for painted surfaces as the paint will come away with the bloodstain

swabbing method

if bloodstain cannot be removed intact, the stain can be swabbed with a sterile swab dampened with distilled water

used as a last resort as wetting the blood may cause degradation of the DNA

if the blood at the scnee is still damp, ideally it should be dried at room temp before packing

liquid blood at a scene can be sampled by soaking onto a sterile swab

cutting method

a section of carpet containing blood stain can be cut out using a sterile cutting device and taken to the lab

blood stained clothing

bloodstained clothing should always be packaged in paper bags which should then be sealed and labelled appropriately

bloodstained clothing should be dry before packaging

clothes are laid out on a flat, clean surface to dry at room temperature

if clothes are packed while wet, the transfer of blood may interfere with the blood pattern or possibility of finding blood

damp bloodstains will deteriorate

what does blood pattern analysis tell us?

location and description of individual stains and patterns

mechanisms that created the stains

direction of a blood droplet was travelling - by calculating the angles of impact

area of origin - location of blow into blood source

type of object used in attack - edged, blunt, firearm etc

minimum number of blows

presence of a subject at a scene

positioning of the victim, suspect and objects during event

the sequence of events

How is BPA done?

interdisciplinary field methods from physics, biology and maths

based on direct evaluation of the crime scene or analysis of colour photographs from CS with a measuring instrument in clear way to provide a scale

other physical evidence is examined - clothing and weapons

medical records, autopsy reports and even post-mortem exams are used

BPA investigator cannot go to the crime scene and must rely on good notes and information from the original investigators

key facts about blood stain pattern analysis

blood is a very uniform material from an aerodynamic standpoint

rheological properties are not affected to any significant degree by age or gender

blood is shed from a body at constant temperature and is normally exposed to an external environment for a short time

atmospheric pressure, temperature and humidity have no measurable effect on the behaviour of blood

BPA Principle 1

the degree of spatter of a single blood drop depends fare more upon the smoothness of the target surface than the distance the drop falls

the more coarse the surface, the more likely the droplet will be ruptured and spatter

a blotter will cause a drop of spatter to a considerable extent at a distance of merely 18 inches, whereas a drop falling over 100 feet will not spatter at all if it lands on glass or other smooth surfaces

the harder and less porous the surface, the less spatter results

BPA Principle 2

the diameter of blood spot is of little or no value in estimating the distance it has fallen after the first 6 to 7 feet

beyond this distance, the change is too slight to be reliable

edge characteristics/scallops of blood spots have no meaning or value unless the effect of the target surface is well known

how bloodstain pattern analysis works

the diameter of the bloodstains increases as the height increases

blood drop shape

the proportions of the drops can reveal the energy involved in disbursing it

the shape of the stain can illustrate the direction in which it was travelling and angle at which it struck the surface

choosing several stains and using basic trigonometric functions, enables us to do a three dimensional recreation of the area of origin from which a blood letting event occurred

passive bloodstains

occur when blood drips from a wound or object

characterised as drops, drips, clots and pools of blood

passive bloodstains are considered to be low velocity bloodstains

low velocity bloodstains generally leave large blood drops

transfer blood stains

occur when a bloody object comes into contact with another object

transfer blood stains - a contact pattern

may be a bloody hand or shoeprint that can be further analysed for fingerprint data or shoe identification

transfer blood stains - a swipe

occurs when a bloody object contacts an object without blood, while a wipe is the opposite

fingerprints in blood

first take a photograph of the fingerprints in situ which should capture all the details required

examine the print carefully with good lighting and take a sample of blood from the area which has no ridge details

be careful to wear a facemask to avoid any contamination and ensure that the heat from the lighting does not bake the blood and cause the DNA to degrade

what is projected blood stains?

blood is projected when force is applied to it.

Types of projected blood stains

arterial spurting

cast off stains

impact splatter

blunt blow spatter

arterial spurting

blood spurting or gushing from a severed artery after an injury

cast off stains

come from a bloody object in motion such as a knife moving back and forth in a stabbing

impact splatter

happens when an object containing blood is hit with some type of force

blow with a blunt object

results in a low or medium velocity spatter stain while a gunshot pattern results in a high velocity spatter stain and will have very smalll blood drops

rules of blood drop shape

if blood drops from short distance, it is 30cm at a 90 degree angle and tends to be circular

if blood falls several feet straight down, the edges become crenelated and farther the distance from, the surface, the more pronounced the crenelation

rules of blood shape 2

if there are many tiny (pin head size) drops with no larger drop, then it may be concluded that the blood spatter resulted from impact

if the source was in motion when the blood leaked or spurted or if the drops flew through the air and hit an angled surface, the drops generally look like stretched out exclamation marks - the end of the stain that has the smallest size blob indicates the direction in which the source was moving

blood stain road mapping

provides evidence that can be used in court

finding the point of origin gives important information as to the injury suffered by the victim

requires significant skill and accuracy

involves collecting photographic evidence at the crime scene, documentation with written notes and measurements along with sketching and video

cast off droplets

cast off droplets produce a tadpole like long narrow stain with a well defined head

the sharper end of these stains always points back towards their origin

because these are satellite spatters travel only a very short distance and the large drop can almost always be traced

point of origin/convergence

by drawing a line through the long axis of a group of bloodstains, the point of origin can be determined

the convergence point is the point where the lines drawn through the group of droplet stains intersect with each other

area of origin

the area in three dimensional space where the blood source was located at the time of the bloodletting incident

the area of origin includes the point of convergence with a third dimension in the z direction

since the z axis is perpendicular to the floor, the area of origin has three dimensions and is a volume

how quickly blood spatters dry depend on

the surface where the blood landed

how much blood is contained in the spatter

the heat and humidity in the crime scene

when blood spatter skeletonise

the outer edges dry first

flaking off and leave a ring around the original diameter of the spatter

dried and clotted blood

although initiallu blood behaves like a liquid, it begins to clot after leaving the body

can occur withing 15 minutes

if some blood spatter are more clotted than others, it can indicate that multiple blows or gunshots occurred over a period of time

if blood spatter contains bits of tissue and bone

points to a high impact spatter

type of tissue can help to determine the depth and severity of the injuries that were sustained in the attack