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Blood Analysis


Autopsies | Blood Analysis | Absorption-elution technique | Kastle-Meyer Colour Test | Luminol Test | Human or Not? Precipitin Test | Blood stain patterns | DNA Fingerprinting | Restriction Fragment Length Polymorphisms (RFLP's) | Short Tandem Repeats (STR) | Entamology | Common Insects | Links


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


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It has largely been replaced by the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.