FORENSIC BIOLOGY 101
Blood Analysis












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At the scene of most violent homicides there is a
 
overwhelming presence of blood- not only on the
 
body of the victim and any murder weapon that
 
may have been left, but if the crime has been
 
commited in a building, on walls, floor, furniture
 
and even the ceiling. Furthermore, suspects are
 
always left with the surprising thought that bleach
 
is unable to kill or eliminate the blod that has been
 
present on clothing, furniture and walls.  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 andpalm-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. 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





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Above: an analysis of Blood Stain on a shirt
(from "The Encyclopedia of Forensic Science")
 
It has largely been replaced by the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.
 
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.  This principle is used to test
 
whether blood-stains are human or not. 
 
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 ina 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. The following
 
web pages provide a thorough explanation of
 
all these techniques.
 

























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