Blood pattern analysis is a helpful tool in forensic science that can aid in crime scene reconstruction. When combined with DNA analysis and other investigation findings, blood evidence can provide more conclusive and detailed details of the sequence of events.
▪ A tool used to understand what may have taken place during blood shedding activities:
▪ What, how, when, how many, where
▪ Possible injuries sustained
▪ Possible weapon used
▪ Minimum number of blows, shots or actions
▪ Sequence of events
▪ An understanding of how blood behaves is essential.
▪ Average person contains 4½ to 5 litres of blood
▪ Blood accounts for ≈ 8% of body weight
▪ Blood is made up of cells and plasma or serum
▪ Plasma or serum is ≈ 55% of blood volume
▪ Cells ≈ 45% of blood volume – comprising red blood
cells (99% of cell volume), white blood cells and platelets
▪ Can loose 10% (≈ ½ litre) with no effect
▪ The loss of 35 – 40% (1¾ – 2 litres) typically fatal
▪ Veins ‘leak’ or ‘ooze’
▪ Arteries carry blood with pressure from the heart and are usually deep within the body to prevent
damage.
Phase 1: Searching and documenting
▪ Searching using white light primarily
▪ Level of search will depend on case circumstances, what is found, and what scenarios need to be
considered.
▪ Will always include looking up and under
▪ Finding blood may direct search in different ways:
▪ Follow trails
▪ Direct attention to bloodstain surfaces, e.g. cupboard doors indicates places searched
▪ Suggest activities to investigate further, e.g. bloodstained towels, sink taps indicates clean up
, Phase 2: Once blood is found and documented the analyst will begin to describe the patterns in terms of
possible mechanisms that may have created them. Opinions always documented separately from the
blood to allow for an independent second check.
▪ BPA is a scientific method where the observations are evaluated against specific questions or
hypothesis
▪ What are the questions you have that you would like to try and answer with BPA?
▪ For example: Witness says it was self defence – does BPA support this?
▪ Witness says there was no weapon used – do the bloodstain patterns support this?
Clasifications:
BPA starts from the shape, size, and distribution of the stains From this the analyst will eliminate certain
mechanisms.
All other possible mechanisms will be included until further information rules them out If there is doubt
about an answer more mechanisms will be included. Analysts MUST NOT over state the evidence.
BPA Categories
Different fields of thought on categories of bloodstain patterns.
Passive stains are sometimes known as non-spatter.
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