Bloodstain Pattern Analysis
Blood stains are presents in various crimes, they are the serological evidence
associated with crimes against persons, including homicide, assault, child abuse,
sexual assault and domestic violence as well as in many property crimes, such as
burglaries, robberies and in arson cases etc. blood stains may be present on weapons
or on tools used in crime. Bloodstains/blood evidence left behind at a crime scene
help the analysts to recreate the sequence of actions that responsible for bloodshed
and draw conclusions as to how the blood may have been shed. Analysts examine
the bloodstains to form opinions about what did or did not happen, he recognize and
examine the size, shape, distribution and location of the bloodstains at a
crime scene.
In Bloodstain pattern analysis (BPA) an analyst uses principles of physics
(cohesion, capillary action and velocity, biology (behaviour of blood) and
mathematics (geometry, distance, and angle) to assist investigators to answer
hidden questions such as -
From where did the blood come/source of the blood?
What caused the wounds?
Direction from where was the victim wounded?
The position of the victim(s) and perpetrator(s) at the time
of incidence.
Movements made by the victim(s) and perpetrator(s) after the
bloodshed?
How many perpetrators were present at the time of incidence?
Does the bloodstain evidence support or refute witness
statements?
Does the evidence sample contain blood?
Is the blood mixed with other biological material?
Some of the bloodstain patterns are –
In a Drip Pattern blood dripped in to a pool of blood on a floor resulting in releasing of droplets from
the pool.
When blood drops released from an object due to its motion creating a bloodstain pattern and it is a cast
off pattern.
When an object striking a blood source below and in front of the vertical surface created an impact
pattern.
Blood evidence provided useful information that help to solve the case and establish a strong link
between an individual and a criminal act, it is very important to correctly document, collect, and
preserve this evidence as it will be presented to a judge or jury several years from the time of the
criminal act. Improperly handling destroys a potential source of facts in a case.
This evidence not only
associated about what happened, but also told what could not have happened.
This information help the investigator in reconstructing the crime,
corroborating statements from witnesses, and including or excluding potential
perpetrators from the investigation. In case of blood it is important to know
that the blood is human or from some other animal. After preliminary
observations are completed you can collect sample from the suspect for
comparison purposes. The physical characteristics of the possible blood stain,
including size, colour, shape, and physical state must be accurately documented
before any chemical or biological testing. Separation of serum and notation of clotting of
the sample if the sample is liquid or semi liquid should also be made at this
time.
Bloodstain analysis has three
broad categories. These three categories are -
Conventional serological
analysis -
This type of testing required a
"large" sample size in good condition for better results and this
testing is rarely statistically individualizing. In this test labs Analysis the
proteins, enzymes, and antigens present in the blood.
Restriction Fragment Length
Polymorphism (RFLP) DNA analysis -
RFLP DNA testing is
statistically individualizing (one out of several million or several billion)
and also usually requires a "large" sample size to obtain significant
results. This test directly analysis the DNA sequences present in the white
blood cells. It is noted that DNA is less susceptible to degradation than
proteins, enzymes, and antigens.
Polymerase Chain Reaction (PCR)
DNA analysis -
This test is not as
statistically individualizing as RFLP analysis and this test works well on
degraded samples and "small" samples. It analysis certain DNA
sequences that have been copied multiple times to a detectable level.
There are two different types of
blood that can be collected at scene of crime –
Liquid and dried blood.
Wet Bloodstains
Liquid blood evidence is
collected from blood pools but it can be collected from clothing of victim and
suspect, using a gauze pad or a sterile cotton cloth. First the sample must be
dried thoroughly at room temperature. It is necessary to be refrigerated or
frozen the sample and brought to the laboratory as quickly as possible..
Small and transportable item
having wet blood after drying, packed in a paper bag (or plastic bag to prevent
contamination of other objects). The bag must be thoroughly air dry.
For Large items or items not
easily transported having wet blood use a 1" X 1" square of the
cotton muslin that absorb the blood and then dried it at room temperature. Pack
it in paper (or plastic).The investigator must collect the samples from unstained
areas of the item for negative controls. Reference blood samples from the victim
and suspect are also needed.
Dried Bloodstains
Dried bloodstains can be found
on larger objects, small objects and on clothing. When bloodstained item is
small and transportable, pack it in a paper bag or envelope. Entire object can
be sent to the lab after properly packaging and labelling. If it is large or
not easily transported, then the following techniques can be used -
Cut out the portion(s) of large
item with the bloodstain(s).Packed it in a separate paper envelope. Control
sample should also be provided if available.
Tape lifting bloodstains – Use
the fingerprint tape and place it over bloodstain. (Do not touch sticky surface
with bare hands). Lift the sample as well as the surrounding control area. A
good contact should be made between the stain and the tape. Place the tape on a
vinyl acetate backing. You can repeat the lifting process several times on the
same stain if necessary. The lifted stain is then labelled and packaged, then
transported to the laboratory.
Scraping bloodstains into a
paper packet - Use a clean sharp instrument to scrape flakes of the bloodstain
into a paper packet and properly labelled it. Do not use a plastic container as
the static charge from the plastic will dispersed the blood flakes and they
stick to the sides of the container.
Absorbing stains onto moistened
1/2" long threads - Use only distilled or deionized water to dampen the
stain before rolling a 1/2" long, number 8, white cotton thread into the
stain. Do not use the threads with bare hands. Place the thread with a pair of
clean forceps or a clean cotton swab. Roll it on the bloodstain, so the stain
is absorbed onto the thread. Placed the threads (and swabs, if used) in a
secure area and allow them to air dry. After drying packed them into a paper
packet and place in an envelope.
Absorbing stains onto moistened
1/2" X 1/2" cotton squares - A white, 100% cotton muslin is used
instead of threads in this process. The muslin will be boiled in distilled or
deionized water and must be air dry before its use.
If dried blood is found on
clothing then the entire cloth should be packaged and labelled and transported
to the lab. The investigator should keep each sample separate so that there is
no contamination between samples.
Suitable reference samples and
unsuitable reference sample -
A suitable reference sample is
collected directly from a person into a tube or "Vacutainer".
An unsuitable reference sample
is bloody clothing or some other bloody item.
The sample must be collected in the proper "Vacutainer."
Different types of "Vacutainers" are -
Yellow Top Vacutainers (contain
Acid Citrate and Dextrose solution)
It is used for conventional
serological testing and DNA testing.
Purple Top Vacutainers (contain
EDTA)
It is used for DNA testing.
Red Top Vacutainers (no
additives)
Used for conventional
serological tests and not very useful for DNA testing. It can be used for
pregnancy and HIV testing.
Grey Top Vacutainers (contain
Sodium Fluoride and sometimes EDTA)
It is used for toxicological
testing. Not suitable for DNA testing and serological testing.
Stored these Vacutainers in a
refrigerator (not frozen) at about four degrees Centigrade until they are
delivered to the crime lab.
For blood visualization Luminol
is used by crime scene investigators. It is a chemical that when applied to
bloodstains will cause the bloodstains to glow in the dark but it has several
drawbacks as it will give false reactions. Rapidly evaporating organic solvents
such as merbromin and ortho-tolidine or water based chemical after treating the
bloody impression with a fixative ( amido black ) are better methods.
Photograph the blood evidence by using colour print film and/or colour slide film. For documenting bloodstains on dark surfaces infrared film can be used. For pertinent bloodstains, overall, medium range, and close up photographs should be taken. When size relevance is significant or direct (one-to-one) comparisons will be made (bloody shoe prints, fingerprints, high velocity blood spatter patterns) then photographs with a ruler next to the evidence is essential. Blood evidence is also documented by drawing a sketch of the crime scene. A sketch must be made if we need spatial relationships of the evidence or to have proportional measurements included in it for calculations (such as blood spatter patterns). Various computer programs are also available for sketching crime scenes and blood spatters. We need to put certain measurement associated with the scene and the individual spatters. Which method or methods of bloodstain analysis are available in public or private labs a crime scene investigator must be know about it.
It is very important for a crime scene investigator that before documenting and collecting blood evidence, he understands the value of this evidence and actually knows about, how it fits in the events associated with the crime. The common points should be considered when dealing with blood evidence are -
Found out the blood with the victim's genetic markers (ABO
blood type, DNA profile, etc.) on the suspect or on the things in the suspect's
possession .Try to found out the blood with the suspect's genetic markers on
the victim or on something associated with the victim.
The investigator should collect representative samples of
the "peripheral" bloodstains, For EX. the bloodstains that are away
from the body and the main area of action, recognize and collect blood spatter
patterns that differ from the majority of the blood spatter patterns. Blood
trails leading away from the scene should also be searched. There is a
possibility that these trails could have originated from a wounded
suspect. Wounds present on suspect body
should be documented and photographed.
In the later investigation the blood samples from the scene
of crime analyzed for those genetic markers that are different in the suspect
and victim.
Used a high intensity light when searching for blood
evidence. A high intensity light source will help in visualization of
bloodstains, even when the stains had been diluted. It is also provide oblique
(side) lighting and this light help for finding trace evidence.
The relationship of various blood spatters and patterns can
be demonstrated by using videotaping of blood evidence. The high intensity
light source make the bloodstains to illuminate and more visible on the
videotape.
Wet evidence either packaged in plastic or in paper always
removed and allowed to completely air dry.
Evidence containing moisture never packed in sealed plastic
or paper containers for more than two hours.
Never exposed the blood evidence to excessive heat or
humidity.
Always take precautionary measures when handling biological
evidence. Always wear protective clothing, gloves, masks etc.
MR. DEEPAK PAWAR has been working as Finger Print Expert / Police Officer in Finger Print Bureau , Delhi Police at New Delhi since 2001 . He is the senior most Finger Print Expert , attending / visited several scene of crime and solved many crime cases .He has passed M.Sc (Chemistry) and he is the Member of International Association of Identification . He is the Member of Delhi Police welfare association . He is supervising the Forensic , New Delhi District , Mobile Crime Team . He is one of the Expert in the Special Investigation Team held for investigation of important cases . He has been giving fingerprint proficient training to Delhi Police personnel's . He has been Presented / giving lectures on topics related to forensic science . He is also making examination paper of Finger Print proficient course . He is awarded with Police Medal by MHA and Delhi Police.