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Blood Pattern Analysis
Bodies of Evidence: Semester 2
Terms in this set (24)
What is blood compromised of?
- Red Blood Cells (Erythrocytes)
- White Blood Cells (Leucocytes)
- Platelets (Thrombocytes)
What are the functions of blood?
transportation, protection, regulation
What are the main features of blood?
- Has viscosity (this is a measure of thickness)
- Non-newtonian liquid (this meaning it thins under stress)
What is Blood Pattern Analysis? and what does it bring to a case?
An interpretation of bloodstain patterns present at a crime scene
As the pattern is a physical image, indicative of the was it was created. The characteristics enables the reconstruction of events
How are blood stain patterns created?
Generated when something comes into contact with a wet source of blood
What external factors affect BPA at scenes?
Heat, Time since deposition, Humidity
What are the 3 types of bloodstains?
Passive, Spatter/ Active, Physically altered stains
What are 3 examples of of Passive Bloodstains?
Blood flows, Pools, Drops, Transfer, Contact (E.g. hair swipes), Free fall
What are 3 examples of Spatter/ Active Bloodstains?
Arterial spurting, Cast off stains, satellite stains
What are 3 examples of Physically altered stains?
Clotted, Dreied, diluted (when a clean up has been attempted), diffused, insects, sequenced, voids
What information can BPA offer to a case?
- The nature of the offence/ Number of strikes
- Location(s) of attacks/ Positions of individuals
- Identification of 'alien' blood
- Support/ Refute Hp/ Hd
- Sequence of events
- Estimates the probability of the offender being bloodstained
Identify 4 limitations of BPA
- It is an interpretation and therefore open to opinion
- Requires experience
- All blood stains need to be identified for an accurate analysis of the scene
- Blood stain trajectory is acred but the calculation used to estimate point of origin and hight/ distance use straight lines
When would items be submitted to labs for blood pattern analysis?
- All seized items (clothing/ weapons)
- If a suspect says they were not present and will therefore not have the victims blood on their clothing
- when individuals say "I was there but not involved" during an affray
(all are observed under magnification)
What are the Presumptive tests for identifying is a sample is blood? (+ the outcome)
- Kastle Meyer (turns pink)
- Leuco-malechite Green, LMG (turns blue/ green)
- Luminol (Fluoresces)
How do presumptive tests work?
They work on the basis of peroxidase reactions causing a colour change in the presences of a sample containing blood.
What are the presumptive tests for identifying if a sample of blood is of human origin?
- Serological Test
- Precipitin Test
What variables affect blood stains and patterns?
- angle of impact
- Nature of target (porous, textured etc)
- Height the droplet falls from (the further it falls the greater the terminal velocity, the greater the size of the stain)
- Volume of blood/ size of droplet
What type of injury and stain will result from a weapon with a small surface area?
Sharp force injuries (e.g. stabbing) = Less blood deposited on the instrument, resulting in smaller, more linear stain patterns
What type of injury and stain will result from a weapon with a large surface area?
Blunt force Injuries (e.g. Hitting/ Beating) = drops of varying sizes and cast off stains which follow the flow of the weapon
What type of blood spatter will result from a gun shot injury?
Mist-like spatter caused by bullets entering and exiting the body
What are the 3 ways in which BPA can be documented?
- Written Notes
What are the 2 ways BPA can be used to recreate a crime scene? with 3 evaluation points for each
- easy to carry out
- works with limited data
- quick and applicable to most crime scenes
- accounts for curvature of trajectory
- results can be viewed from any perspective
How is the blood stains angle of impact determined?
Sin^-1 (W/ L)
How is the distance travelled by the stain calculated?
Distance = (Height/ Tan x angle of impact)
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