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When police have a strong suspect in a murder case, the
temptation is to leave it at that, to close down the search for a
killer. But a few blood samples submitted to tests in the forensic
laboratory can change the entire case!
Good blood cannot lie, they say. Nor can bad. As the
distinguished forensic expert Alixtair R. Brownlie (Solicitor
Supreme Courts, Edinburgh. Scotland) put it to Britain's Forensic
Science Society: "Since Cain slew Abel, spilt blood had borne its
mute testimony in crimes of violence. Stains of blood and body
fluids still play an important part in crime detection, a lesser but
increasing part in the proof of guilt…” And not only the nature and
grouping of stains, but their position at the scene of the crime can
be revolving and is now recognised as a vital piece of evidence in
itself.
The investigation of blood at a crime scene can be broadly
divided into a biological approach (serology) and a physics
approach (blood splatter or bloodstain pattern interpretation). This
fact file will concentrate on the serological approach to blood
evidence. Another fact file will cover the bloodstain
pattern interpretation.
Blood is not the only body product, which can be of use to the
forensic blood grouper. The word serology comes from the ancient
Sanskrit sara, meaning, "to flow". Today it is known that every
fluid, which flows in the human body, can be identified: sometimes
to prove the guilt of a suspected person, but also very often to
protect the innocent. .
Essentially, forensic serology is based upon facts known vaguely
since the dawn of time, and with much more certainty since in1628
the English physician William Harvey discovered the circulation of
blood. Christopher Wren is said to have experimented with
transfusion, and in his diary Samuel Pepys recorded that a donor was
paid a sum of 20 shillings (about $500 in 1974 money), as well as
speculating what would happened "were the blood of a Quaker to be
let into an Archbishop". For centuries the English aristocracy were
genuinely believed to be born with blue blood, and boasts such as
"the blood of an Englishman" were taken seriously.
Then, in 1930, the Viennese doctor Karl Landsteiner received a
Nobel Prize award for his research into serology. He had announced
to the scientific world that all human blood could be grouped into
four main types. His work stimulated other biologists. Today for
convenience the groups are known as O, A, B and AB.
Expert Evidence
While it should be remembered that it is never possible to say
"this bloodstain originated from this person"; nevertheless it may
be possible to conclude, "this bloodstain cannot have originated
from that person". A defence case may depend on this crucial fact.
One striking example came to light early in September 1961 in
England, when a 24 year old army private at Aldershot was cleared of
sexual attack on a 38 year old mother.
"I can't remember exactly what happened," the woman said to the
police "He jumped on me and got hold of my shoulders. I screamed as
hard as I could ….. Then somehow I found I was at the bottom of a
steep bank, and my little daughter was crying. The man had pulled
off my blouse, but I gave up the struggle because he twice
threatened to hurt my child .."
False Identification
The doctor who examined the woman later confirmed there had been
an attack. A solider was picked out at an identification parade, and
charged with rape. Bryan Culliford, from the New Scotland Yard
Laboratory, demonstrated that tests proved the suspect was in Group
B, while the stains on the unfortunate woman were Group A. "We find
there is no case to answer" announced the chairman of the court.
In her distressed state, the woman had picked out the wrong man
at the identification parade. But for serology and its forensic
application an innocent man could have been sent to jail.
Blood continues to play an important
part in forensic investigations, and the discovery of new antibodies has enabled
blood grouping techniques to be further refined. For example the
Kell antigen is
virtually confined to the white population, whereas the Duffy
antigen is completely absent. Thus, blood grouping characteristics
can be used to give an indication of race, and help to pinpoint the
origin of bloodstains.
Forensic laboratories have researched
sophisticated techniques for analysing protein in blood, and have
been able to produce blood profiles with the prospect of
establishing unique blood "fingerprints". While this remains for the
moment a serologist's dream, blood continues to give up its secrets,
and has described it as 'a treasure trove of hidden clues'.
The first task in examining
suspicious stains is to determine whether they are blood, and if so,
are they human? Once this is established stains are examined for
age, sex and blood group. The shape and pattern of liquid
blood-splashes can help in reconstructing the murder; bloody
fingerprints and palm-prints tell their own story; dried blood on a
suspect's clothing can be related to the victim, the crime scene and
the murder weapon; blood and tissue forced under the fingernails of
the victim during a violent struggle can be linked to the assailant.
Thus a single blood-trace can provide
a wealth of information, and analytical techniques are improving all
the time. For example, traces of drugs found in a
bloodstain indicate medical treatment which a person might be
receiving. While such procedures improve the scope of
detection, it is not yet possible to identify an individual by his
blood as it is by his fingerprints. Nevertheless, forensic serology, which in
addition to blood deals with other body fluids such as saliva and semen, is important not only
for narrowing suspicion on the guilty but also in showing a
suspect's innocence. As in many other aspects of forensic
investigation, bloodstains are taken into account with a variety of
other evidence to build up a pattern of crime.
A number of substances such as
fruit-stains or dye-stuff may soil clothing and take on the
appearance of bloodstains. The benzidine test - used for many
years to confirm the presence of blood - has been discontinued
because the reagent is carcinogenic.
It has largely been replaced by the Kastle-Meyer test, using a
solution of phenolphthalein which turns pink in contact with even
small traces of blood. The test works by detecting the
presence of the enzyme
peroxides in the blood. However, as this substance is also
present in other biological materials, the Kastle-Meyer test is
regarded as a screening procedure. It is highly
sensitive, and positive reaction is judged presumptive of blood, and
further confirmatory tests are carried out. These are
usually chemical and microscopically procedures to identify blood by
its pigments and cellular structures.
Once a stain has been confirmed as
blood it has to be determined whether it is human or animal.
The precipitin test is used for this purpose. Blood of every
animal species contains different proteins, and blood from one
species will not accept proteins from a different species.
Blood develops antibodies as a
protective measure against disease and foreign matter to render them
harmless. The serum
containing antibodies produced by this reaction provides immunity
from disease.
This principle is used to test
whether blood-stains are human or not. Serum for the precipitin test
is obtained from rabbits which have produced antibodies to destroy a
small quantity of human blood injected into them. A drop of
this anti-human serum is added to suspect blood, which will
precipitate its protein if it is of human origin. Police
laboratories hold anti-sera for most common animals, thus allowing
the crime investigator to confirm or disprove statements made by the
suspects about he origin of suspicious bloodstains. The
precipitin test is sensitive, and will work on small traces of
blood. The test is also known as the Uhlenbuth test after the
German scientist who developed it in 1901.
The colour of dried blood changes in
time from red to brown, and the peroxidise test takes longer to
develop with an old stain. An experienced observer considering
these factors might be able to give an opinion as to the age of a
particular stain, but it is now possible to measure colour-change
scientifically. Spectrophotometric
analysis of bloodstains allows them to be aged within the range of
one day to three weeks.
In 1949 two British scientists
observed that the nuclei in the cells of female tissues usually
contained a distinctive drumstick - like structure which was rare in
males. This structure called a Barr bodies after one of its
discoveries, is most noticeable in white blood cells and in the
epithelial cells lining the mouth. Barr bodies are
associated with the differences in chromosomes between
males and females, and their appearance in blood of unknown origin
is a basis for identifying it as from a female.
Determination of the blood group
characteristics of stains found on clothing or a suspected murder
weapon is another powerful link in the chain of evidence that can be
built up in a case of violent death. Blood grouping is a
developing science in its own right, and while it cannot provide
information as certain as a fingerprint, it can provide
circumstantial evidence establishing contact between a suspect and
the victim.
Every person's blood falls into one
of the four international blood groups identified in 1900 by Dr Karl
Landsteiner. The ABO blood grouping system is a function of
the red blood cells, and the presence in them of a substance known
as agglutinogen. A
Group contains A agglutinogen B Group has B agglutinogen, AB Group
contains both and O Group has neither. (What
are anti-body reactions?) These factors are found in specific
proportions among different populations.
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FREQUENCY OF BLOOD
GROUPS IN AUSTRALIAN POPULATION
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|
O
positive
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40%
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|
O
negative
|
9% |
| A
positive
|
31% |
| A
negative
|
7%
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B
positive
|
8%
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B
negative |
2% |
| AB
positive |
2%
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AB
negative
|
1%
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What
about other ethnic groups?
In 1927 Dr Landsteiner and a
fellow-worker discovered further factors which occurred separately
in human blood and were distributed in specific proportions among
the population. These are the M. N. and MN factors, to which
was added the P factor and in 1940 the Rhesus factor. The
knowledge that each person's ABO and MN blood group characteristics
are inherited and fixed for life has made the examination of blood
an important part of crime investigation. It is possible to
place an individual in one of 288 different blood groupings, but
forensic serologists are not able to say that a particular blood
trace originated in a particular individual. The value of
blood grouping procedures in crime work is that many potential
suspects can be eliminated from an inquiry, thereby allowing the
investigation to be narrowed down. About 80 per cent of the
population are secretors which means
that their blood cells are present in such body fluids as semen and
saliva. It is possible, therefore, to determine blood
groupings by examining these fluids.
Blood test
In criminology scientists do concern themselves with medical
matters such as agglutination, but primarily the vital question
involves whether or not a sample is blood. A minute sample in
the laboratory is extracted from the stained material kept in a
saline solution, and a tiny drop of the extract is mixed with a
solution containing phenolphthalein and potassium hydroxide,
powdered zinc and hydrogen peroxide. If this test is negative (no
change), the sample cannot be blood. If the mixture shows a
clear pink colour, it is blood.
Biologists sometimes use a different test, in which glacial acid
is added to a solution of hydrogen peroxide and benzidine - a drop
of this being added to the test sample, which immediately turns a
deep blue if there is blood present. The next step is to use
an antiserum prepared in an animal, which will react specifically
with human blood, thus demonstrating whether the sample is of human
origin.
"The blood of an Englishman" is not a subject over which forensic
serologists wax racialist, because crime is international. The
frequencies of the various genes within different blood group
systems may, however, vary from race to race and could possibly
provide important evidence. Blood group systems in general
have acquired names such as Kidd, Duffy and Kell after the
patients in whom the antibodies were first discovered, and all of
them, of course, allow scientists to narrow down the field.
Summarizing all the international work of forensic serologist,
the late Dr F.I.N. Dunsford, Ph.D. of Britain's National Blood
Transfusion Service, stressed that, in crime detection, the
"usefulness" of a blood group system is the measure of its
efficiency - differentiating the red cells of one person from those
of another.
From his tests, for example, it is known that the Rhesus antigen
V is present in fewer than 0.5 per cent of white people, but present
in 40 per cent of West African Negroes. The chromosomes (the
rod like structures which show as pairs in every developed cell)
known as cDe are also more common among Negroes than whites.
The Duffy phenotype Fy is always completely absent from whites,
but present in 90 per cent of West Africans. Kell antigen is
virtually confined to white races, while Diego positives are
virtually absent from whites, yet present in Caribe Indians,
Japanese, and Chinese.
At the extreme of the blood group sis a certain LU (a _ b__)
factor, which many serologists believe to be so rare that an
estimated total of only eight people among the world's 3200 million
plus can have it. One of the eight, a Sheffield ( England
) woman, had three pints of the rare blood
flown to her in a British hospital from an American donor.
More on blood type systems.
However, researchers maybe only on the threshold of discoveries
in investigation of body fluids. It is now nearly 75 years
since serologists put blood samples under the microscope and found
the elements which are freely suspended in the plasma -
essentially the erythrocytes (red corpuscles), leukocytes (white
corpuscles), and the blood platelets (egg shaped and circular bodies
suspended in the straw plasma more commonly known as the
"serum").
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