crime scene reconstruction
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Crime Scene Reconstruction. Glass . Blood. Laminated Glass . - PowerPoint PPT PresentationTRANSCRIPT
Crime Scene Reconstruction
Glass Blood
Laminated Glass
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.
Tempered Safety Glass
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.
Annealed/Ordinary Glass
Although annealed (ordinary) glass is probably the most common glass around, it also has the potential to be the most dangerous. When annealed glass breaks, it produces razor-sharp shards of glass that can cause terrible injury. Building codes in many parts of the world restrict the use of annealed glass in areas where there is high risk of breakage and injury, for example in bathrooms, in door panels, fire exits and at low heights in schools.
Glass Fracture from Bullets
Blood Stain Patterns
• 1. Low Velocity Impact– Droplets– Cast offs2. Medium Velocity Impact- Spatter from weapon’s impact- Arterial spurts3. High Velocity- Spray from weapon exiting body- Exhalation of blood
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
• 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
• 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
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
90
10
70
2030
60 50 40
Adapted from Introduction to Forensic Sciences,W. Eckert, CRC, 1997
80
Gravitational dense zoneat lower edge
14
Point of Origin
length
width
Angle of impact = arc sin W/L
Distance from point of convergence
Heig
ht a
bove
poi
nt o
f con
verg
ence
Origin
85 60 45 30
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
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Drip Pattern• Free-falling drops dripping into wet blood• Large irregular central stain• Small round & oval satellite stains
.. .......
Drip 2
Blood dripping into itself from height of 1 m (8 drops)
39
Dripping onto steps
Wave Cast-off
.Parent drop
wave cast-off
Tail of wave cast-off points back to parent drop
Tail of elongated stain points in direction of travel
Medium Velocity Blood Spatter
•Blows with weapon (e.g. baseball bat)
Downswing of Hammer
Cast-off from Weapon
ceiling
Overhead swing with bloodied metal bar
Cast-off PatternHow many strikes?
Cast off Patternans: 4 (first strike causes bleeding)
1
2
3
Cast off Pattern How many strikes?
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.
Three overhead swings with hatchet
Cast-off Pattern? Object
Cast-off Patternfrom Hand
Cast-off pattern from bloodied hand swung in front of target
6” ruler
Cast-off & medium velocity spatter
Cast-off & medium velocity spatter 2
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
spatter
broken pottery
Neck incisions (scene)
Neck incisions
Thyroid cartilage
Probe in carotid artery
‘Hesitation’ injuries
Medium velocity blood spatter.Point of impact 15 cm in front of vertical target surface
6” ruler
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 spatterBloodstained foam held just above target surface.
Back-spatter on entry
Forward spatteron exit
bullet
Bullet passing L to R just above sheet
Bullet enters foam
bullet exits foam
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
Back spatter on steadying
hand
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 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• Blood flows horizontally & vertically• Altered by contours, obstacles• Often ends in pool
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
Flow pattern