Bloodstain Evidence Bloodstain Evidence May reveal: May 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 1
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Bloodstain Evidence May reveal: Origin(s) of bloodstain Distance of bloodstain from target Direction from which blood impacted Speed with which blood.
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• 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
1
Liquid BloodLiquid Blood• Physical properties
– viscosity
– surface tension
– specific gravity
• Behaves as a projectile in motion– biology, physics, maths
2
Blood lab 1
• We measured the diameter of blood drops from different heights
• Whiteboard now:– What was the independent variable?– What was the dependent variable?– What type of graph did we use and why?
Surface TensionSurface Tension
• Resistance to penetration & separation• Surface acts to reduce surface area
• Smallest SA to Volume ratio is offered by sphere
3
Dripping BloodDripping Blood
Blood drop grows until Wt (G) > S.T.
Single drop breaks free (teardrop shape)
Surface tension pulls in vertically
Shape settles into sphere (0.05 ml)
Does not break up until impact
And horizontally
Blood trickles downwards
4
Drop size
.
Standard drop size 50ul (0.05ml)
.
Rapid bleeding gives slightly larger drop
Shaking/movementcasts off smaller drops
.
5
Terminal Velocity v Distance Fallen(metric)
Terminal velocity as a function of distance fallen (metric)
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5 6 7
Fall distance (m)
Ter
min
al v
elo
city
(m
/s)
6
Terminal Velocity v Distance Fallen(imperial)
Terminal velocity as a function of distance fallen (imperial)
0
5
10
15
20
25
30
0 2 4 6 8 10 12 14 16 18 20
Distance fallen (f)
Te
rmin
al v
elo
cit
y (f
/s)
7
Free Falling Blood Droplets
.
50 ul4.6 mm
7.5 m/s
4.2 to5.4 m
0.5 ul2.12 mm
2.4 to 3 m
.4.6 m/s
0.12 ul1.32 mm
0.84 to 1 m
.3.3 m/s
0.06 ul1.1 mm
0.5 to 0.65 m
.2.2 m/s
8
Shape & Size of BloodspotShape & Size of Bloodspot
• Depends mostly on nature of target surface– texture (rough or smooth)– porous or non porous
• Size is related to distance fallen, provided:– standard 50 ul drop of blood
• There is little change in spot diameter beyond a fall distance of 1.2 m
9
Height FallenHeight 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
10
Blood Lab 2
• We looked at how different surfaces affect the blood splatter
• Whiteboard now:– What was the independent variable?– Dependent variable?– Control?– What kind of graph did you use and why?
Effect of Target SurfaceEffect of Target Surface
. .... .Spreads out smoothly ST of spreading edge is
broken by irregular surface
11
Experiments with Falling Blood DropletsExperiments with Falling Blood Droplets
blood
dropper
ruler
Terazzo floor
whiteboard
rough paper towel
paper
Fabric (theatre green)
Height
Target Surface
12
Height/Surface
Single drop of blood falling from various heights (m) onto various surfaces
smooth floor paper towel fabric
0.5
1
2
3
0.5
1
2
3
13
Blood Lab 3
• We looked at direction of blood splatter
• Whiteboard now:– What was the independent variable?– Dependent variable?
– CSI video
Blood Lab 4
• We looked at how angle has an effect on blood drops
• Whiteboard now:– Independent and dependent variable?– Name 2 characteristics you noticed of the blood
spatter relative to angle
Angle of Angle of ImpactImpact
90
10
70
2030
60 50 40
Adapted from Introduction to Forensic Sciences,W. Eckert, CRC, 1997
Tail of elongated stain points in direction of travel
15
Point of ConvergencePoint of Convergence16
Point of ConvergencePoint of Convergence5 ml blood squirted from a syringe from height of 1 m
17
Point of OriginPoint of Origin
length
width
Angle of impact = arc sin W/L
Distance from point of convergence
Hei
ght a
bove
poi
nt o
f co
nver
genc
e
Origin
85 60 45 30
181
Tracing Origin of Tracing Origin of BloodspotsBloodspots
• Point of convergence method– 2 dimensional image
• Point of origin method– adds 3rd dimension to image
• In practice:– use of string & protractor at scene
– use of computer at laboratory
19
Blood SpatterBlood Spatter
• Low velocity (5 f/s, 1.5 m/s)– e.g. free-falling drops, cast off from weapon
• Medium velocity (25 - 100 f/s, 7.5 - 30 m/s)– e.g. baseball bat blows
• High velocity (>100 f/s, 30 m/s)– e.g. gunshot, machinery
20
Herbert Leon MacDonell,
Laboratory of Forensic Science,P.O. Box 1111,Corning,New York,14830,USA
21
Cast-off from WeaponCast-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
23
Downswing of HammerDownswing of Hammer
24
Cast-off from WeaponCast-off from Weapon
ceiling
25
Overhead swing with bloodied metal bar26
Cast-off Pattern (1/2)Cast-off Pattern (1/2)
27
Cast off Pattern (2/2)Cast off Pattern (2/2)1
2
3
28
Cast off Pattern (2/2) Cast off Pattern (2/2) ? Sequence? Sequence
29
Cast off Pattern (2/2) Cast off Pattern (2/2) ? Sequence? Sequence 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.
30
Three overhead swings with hatchet
31
Cast-off & medium velocity spatter32
Cast-off & medium velocity spatter 233
Cast-off PatternCast-off Pattern? Object? Object
34
Cast-off PatternCast-off Patternfrom Handfrom Hand
35
Cast-off pattern from bloodied hand swung in front of target
6” ruler
36
.... ...
..
...
Drip PatternDrip Pattern
• Free-falling drops dripping into wet blood• Large irregular central stain• Small round & oval satellite stains
.. .......
37
Drip 1:Drip 1:
Blood dripping into itself from height of 1 m (8 drops)
38
Drip 2Drip 2
Blood dripping into itself from height of 1 m (8 drops)
39
Dripping onto steps
40
Splash onto vertical surface
6” ruler
10 ml blood thrown 1 m onto a vertical target surface
45
Stamping in blood 1
Area seen in close-up in next slide
46
Stamping in blood Close-up of heel area
47
Stamp 1Stamp 1
Blood pool (10 drops) before stamping
48
Stamp 2Stamp 2
Blood pool (10 drops) after stamping49
Arterial Spurt PatternArterial Spurt Pattern• Blood exiting body under arterial pressure• Large stains with downward flow on
vertical surfaces• wave-form of pulsatile flow may be
apparent
50
Small arterial spurt
spatter
broken pottery
51
Neck incisions (scene)52
Neck incisions
Thyroid cartilage
Probe in carotid artery
‘Hesitation’ injuries
53
Medium Velocity Medium Velocity Blood SpatterBlood Spatter
Medium velocity blood spatter.Point of impact 15 cm in front of vertical target surface
6” ruler
55
Flick 1:Flick 1:
Blood flicked between middle finger & thumb onto a vertical smooth surface from a distance of 15 cm
56
Flick 2:Flick 2:
Blood flicked between middle finger & thumb onto a vertical smooth surface from a distance of 15 cm
57
High Velocity Blood SpatterHigh Velocity Blood Spatter• Blood source subjected to HV impact
– > 100 f/s, 30 m/s
• Fine mist: spot size < 0.1 mm• Small mass limits spread to 1 m• !Some larger droplets reach further• Gunshot
– back-spatter from entry wound– forward spatter from exit wound
• High speed machinery
58
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
59
Gunshot Back SpatterGunshot 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
60
Back spatter on steadying
hand
61
Gunshot Forward SpatterGunshot 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
62
Forward spatter (5 ms after bullet impacted at 1000 f/s)
2.5 cm
blood soaked target
bullet
63
6” ruler
Forward spatter onto target placed 15 cm behind point of HV bullet impact (bullet passing towards screen) 1
64
Forward spatter (closer view)65
Forward spatter (closest view)
5 mm
66
Wipe PatternsWipe Patterns• Object moves through a wet bloodstain• Feathered edge suggests direction
67
Transfer PatternsTransfer 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
68
Transfer from hair (hair-swipe) 1
69
Transfer from hair (hair-swipe) 2
70
Flow PatternsFlow Patterns• Blood flows horizontally & vertically• Altered by contours, obstacles• Often ends in pool