Crime Scene Reconstruction

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

.... ...

..

...

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