Forensic Biology > Bloodstain Pattern Analysis > Flashcards

Bloodstain Pattern Analysis Flashcards

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1
Q

bloodstain pattern analysis

A

an in-depth evaluation of bloodstain pattern

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2
Q

factors to consider in bloodstain pattern analysis

A
  • size
  • shape
  • number
  • dispersion
  • volume
  • location
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3
Q

what does BPA define?

A

the nature of the action that created it

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4
Q

determinations from blood stains

A
  • height of impact
  • direction of travel
  • angle of impact
  • nature of the force
  • relative positions of individuals at a scene
  • the sequence of events may have occurred
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5
Q

Dr. Eduard Piotrowski

A
  • first known, systematic study of bloodstain pattern
  • concerning the origin, shape, direction, & distribution of the bloodstains
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6
Q

Victor Balthazard

A
  • explained Forensic Medicine importance to Congress
  • recognized empirical relationship of stain shape to angle impact
  • introduced the ‘stringing concept”
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7
Q

Herb MacDonell

A
  • published seminal studies & provided the first training
  • flight characteristics & stain patterns of human blood
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8
Q

SWGSTAIN

A

mission to promote and enhance the development of forensic bloodstain pattern analysis practices through collaboration of government forensic laboratories, law enforcement, private industry, and academia

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9
Q

what is blood affected by?

A
  • gravity
  • surface tension
  • viscosity
  • air resistance
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10
Q

what holds a blood droplet together in flight?

A

surface tension

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11
Q

gravity is consistent =

A

blood in flight in consistent

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12
Q

viscosity

A

the resistance to flow

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13
Q

what is the effect of air resistance dependent on

A

droplet size

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14
Q

the smaller the droplet …

A

the greater the force effect

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15
Q

does blood spontaneously breakup?

A

not unless it is acted upon by an external force

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16
Q

what path does blood take?

A

the path of least resistance

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17
Q

what special property does blood have?

A

an adhesive property

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18
Q

Pattern Diversity Principle

A

combination of blood volume and forces acting on those volumes results in recognizable classes of patterns

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19
Q

Principle of Stain Shape & Vector

A

the shape of the bloodstain provides indicators as to the direction of deposition & spatial origin of the blood

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20
Q

Physically Altered BPA Principle

A

exposed blood will react to environmental conditions in a predictable manner

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21
Q

what force produces a high velocity blood splatter?

A

an external force greater than 100 feet/sec

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22
Q

high velocity blood splatter stains

A
  • sometimes referred to as a mist
  • tend to be less than 1 mm
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23
Q

what creates high velocity blood splatter?

A
  • usually created by gunshots or explosives
  • may result from industrial machinery or expired air (coughing or sneezing)
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24
Q

high velocity blood splatter travels

A

travels the shortest distance because of the resistance of the air against their small mass

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25
what force produces a medium velocity blood splatter
an external force between 5 feet/sec and 25 feet/sec
26
medium velocity blood splatter stains
generally measure 1 to 3 mm
27
what creates medium velocity blood splatter?
- blood flying from a body to a surface as a result of blunt or sharp force trauma - body colliding with rounded or edged surfaces/vehicles
28
what creates a low velocity blood splatter?
an external force less than 5 feet/sec (normal gravity)
29
low velocity blood splatter stains
generally 3 mm and larger
30
what causes a low velocity blood splatter?
- blood dripping from a person walking or running - bloody weapon
31
low velocity blood splatter drips
dripping blood often falls at a 90° angle & forms a 360° (circular) stain when it hits a flat surface
32
3 types of bloodstains
- passive - splatter - altered
33
example of passive bloodstains
gravity
34
example of spatter bloodstains
energy applied creating flight
35
example of altered bloodstains
physically/environmentally altered
36
passive blood stains
- drop(s) - flow - large volume
37
spatter bloodstains
- impact mechanism - secondary mechanism - projection mechanism
38
secondary mechanism
spines & satellite stains
39
satellite stains
smaller bloodstain originating from a larger blood stain
40
altered bloodstains
- time lapse - diluted - diffused - insects - contact - voids
41
wipe
moving through a pre-exisiting blood stain
42
swipe
transfer from a blood bearing surface
43
the basic premise of BPA theory
based on stain size, shape, volume, orientation, & other physical characteristics, the analyst can differentiate between basic types of blood shed events
44
what must an analyst do to support any claim about a pattern?
must be able to articulate what characteristic led him to his decision
45
BPA scientific process/method
- data collection/gather case information - segregate patterns, then categorize the patterns - documentation, notes of sizes, shapes, directionality, areas or origin, etc - evaluate different hypotheses - test different theories - conclusions/results, supported by physical evidence - peer reviewed
46
area of convergence
the area containing the intersections generated by lines drawn though the long axes of individual stains (2D)
47
a longer blood stain is formed by
a lower angle of impact
48
what increases spatter diameter?
height
49
when do spines appear at the edge of a stain?
when blood drops come from greater heights
50
direction of tail =
direction of blood
51
equation: angle of impact
sin theta = width / length
52
determining the area of origin
- 3D location from which spatter originated - using the stringing method
53
presumptive test
- indicates possible presence of a substance - "this is likely saliva"
54
confirmatory test
- conclusively identify a substance - "this is definitely human saliva"
55
pros of presumptive test
- narrow possibilities & helps to decide which test to do next - can use on large areas - can locate evidence not visible with the naked eye - cost effective - portable - sensitive
56
cons of presumptive test
many false positives
57
pros of confirmatory test
- conclusively identify a substance - wont waste money when moving on to DNA testing - MUCH smaller risk of false positives
58
cons of confirmatory test
- higher cost - require additional equipment - takes longer
59
screening for bodily fluids - when not readily apparent
- many body fluids fluoresce under a black light - things that fluoresce contain phosphors
60
body fluids that fluoresce
- urine - saliva - sweat - semen
61
phosphors
substance that absorbs energy outside of the visible spectrum & re-emits the energy as visible light
62
blood under a black light
- does not fluoresce - it sometimes appears darker
63
Human Blood Presumptive tests
- Kastle Meyer Test - Luminol - Alternate Light Source
64
Human Blood Confirmatory tests
- Precipitin test - Hematrace - does not confirm DNA presence
65
quality control
are the tests running properly?
66
quality assurance
does the whole program work?
67
negative control
not expected to produce results
68
positive control
expected to produce results
69
what should be a positive control?
where blood is present
70
what should be a negative control?
where blood isn't present
71
Presumptive Blood Tests (Luminol & Phenolphthalien)
- uses hemoglobin to catalyze the oxidation of certain reagents - hydrogen peroxide often used as oxidizing agent - visible as a color change
72
Confirmatory Human Blood Test
- Precipitin Test - ABAcard Hematrace
73
ABAcard Hematrace
- remove a piece of fabric/swab with suspected blood - add to provided vial (containing buffer) & shake - remove liquid from vial & put two drops in the same wells
74
Human Semen Presumptive Tests
- Acid Phosphatase - Prostate Specific Antigen
75
Human Semen Confirmatory Tests
- look under a microscope for morphology and stains - look for christmas tree in sperm
76
Acid Phosphatase Test
- presumptive test - semen will produce a positive color change in < 1 minute - affected by concentration & age of stain
77
presumptive & confirmatory tests - Saliva
based on the presence of saliva alpha amylase
78
Saliva Presumptive Test
Phadabas
79
Saliva Confirmatory Test
RSID (Rapid Stain Identification) Test
80
neutralization test
if AB antigens are present in the fluid they will react with (neutralize) antibodies, so that they don't interact & agglutinate red blood cells with the same antigen
81
saliva + antibody A + A Type RBC = no agglutination
saliva from a secretor of A saliva
82
saliva + antibody A + A Type T RBC = agglutination
saliva from a non-secretor or saliva from a secretor without A type RBC
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