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Crime Scene Reconstruction. Glass . Blood. Laminated Glass .

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Presentation Transcript
slide3
Laminated Glass is made up of a vinyl laminate (PVB) layer bonded together between two panes of glass under heat and pressure. Laminated glass may crack upon impact, however the glass fragments typically stick to the protective inter-layer rather than falling free and potentially causing injury. It breaks exactly like the windshield of your car, cracks but is held in place by the vinyl laminate layer.
slide5
The "heat-treatment" process of tempered glass provides safety characteristics giving it additional strength, resistance to thermal stress and impact resistance. Additionally, when fully tempered glass breaks it fractures into small, relatively harmless fragments. And markedly reduces the likelihood of injury to people as there are no jagged edges or sharp shards.
blood stain patterns
Blood Stain Patterns
  • 1. Low Velocity Impact
    • Droplets
    • Cast offs

2. Medium Velocity Impact

    • Spatter from weapon’s impact
    • Arterial spurts

3. High Velocity

    • Spray from weapon exiting body
    • Exhalation of blood
bloodstain evidence may reveal
Bloodstain EvidenceMay reveal:
  • Origin(s) of bloodstain
  • Distance of bloodstain from target
  • Direction from which blood impacted
  • Speed with which blood left its source
  • Position of victim & assailant
  • Movement of victim & assailant
  • Number of blows/shots
blood spatter
Blood Spatter
  • Low velocity
    • e.g. free-falling drops, cast off from weapon
  • Medium velocity
    • e.g. baseball bat blows
  • High velocity
    • e.g. gunshot, machinery
low velocity blood spatter
Low Velocity Blood Spatter
  • Blood source subjected to LV impact
  • Spot diameter: mostly 4 - 8 mm
    • some smaller, some larger
  • Free-falling drops (gravity only)
  • Cast off from fist, shoe, weapon
  • Dripping
  • Splashing
  • Arterial spurting
height fallen

Height Fallen

Single drops of blood falling from fingertip onto smooth cardboard from various heights.

No change in diameter beyond 7 ft.

Adapted from

Introduction to Forensic Sciences,

W. Eckert, CRC, 1997

angle of impact
80

90

10

60

50

40

70

20

30

14

Angle of Impact

Gravitational dense zone

at lower edge

Adapted from

Introduction to Forensic Sciences,

W. Eckert, CRC, 1997

point of origin
Origin

Height above point of convergence

85

60

45

30

Distance from point of convergence

length

Point of Origin

width

Angle of impact = arc sin W/L

cast off from weapon
Cast-off from Weapon
  • First blow causes bleeding
  • Subsequent blows contaminate weapon with blood
  • Blood is cast-off tangientially to arc of upswing or backswing
  • Pattern & intensity depends on:
    • type of weapon
    • amount of blood adhering to weapon
    • length of arc
drip pattern
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Drip Pattern
  • Free-falling drops dripping into wet blood
  • Large irregular central stain
  • Small round & oval satellite stains

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wave cast off
Tail of elongated stain

points in direction of travel

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Tail of wave cast-off points

back to parent drop

Parent drop

wave cast-off

Wave Cast-off
medium velocity blood spatter
Medium Velocity Blood Spatter
  • Blows with weapon (e.g. baseball bat)
cast off pattern ans 4
Cast off Pattern ans: 4

1

(4 spots)

2

(3 spots)

3

(2 spots)

If weapon does not pick up more blood, spatter from subsequent backswings becomes progressively less.

In practice weapon picks up more blood with each successful blow.

arterial spurt pattern
Arterial Spurt Pattern
  • Blood exiting body under arterial pressure
  • Large stains with downward flow on vertical surfaces
  • wave-form of pulsatile flow may be apparent
small arterial spurt
Small arterial spurt

spatter

broken pottery

neck incisions
Neck incisions

‘Hesitation’ injuries

Probe in carotid artery

Thyroid cartilage

medium velocity blood spatter point of impact 15 cm in front of vertical target surface
Medium velocity blood spatter.Point of impact 15 cm in front of vertical target surface

6” ruler

high velocity blood spatter
High Velocity Blood Spatter
  • Blood source subjected to HV impact
  • Fine mist
  • Some larger droplets reach further
  • Gunshot
    • back-spatter from entry wound
    • forward spatter from exit wound
  • High speed machinery
gunshot back forward spatter
bullet exits foam

Bullet enters

foam

bullet

Gunshot: back& forward spatter

Bloodstained foam held just above target surface.

Bullet passing L to R just above sheet

Back-spatter

on entry

Forward spatter

on exit

gunshot back spatter
Gunshot Back Spatter
  • Arises from entrance wound
  • Passes back towards weapon & shooter
  • Seen only at close range of fire
  • Seen on:
    • inside of barrel
    • exterior of weapon
    • hand, arm, chest of shooter
gunshot forward spatter
Gunshot Forward Spatter
  • Arises from exit wound
  • Passes forwards in same direction as shot
  • More copious than back-spatter
  • Can be seen at any range of fire
  • Seen on nearby surfaces, objects, persons
    • especially on wall behind victim
gunshot forward spatter1
Gunshot Forward Spatter
  • Arises from exit wound
  • Passes forwards in same direction as shot
  • More copious than back-spatter
  • Can be seen at any range of fire
  • Seen on nearby surfaces, objects, persons
    • especially on wall behind victim
flow patterns
Flow Patterns
  • Blood flows horizontally & vertically
  • Altered by contours, obstacles
  • Often ends in pool
transfer patterns
Transfer Patterns
  • Wet, bloodied object contacts a secondary surface
  • Transfer from:
    • hand, fingers
    • shoes, weapon
    • hair
  • Transfer to:
    • walls, ceilings
    • clothing, bedding
  • Produces mirror-image of bloodied object
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