Upload
edward-ball
View
222
Download
0
Embed Size (px)
Citation preview
Blood Spatter & Crime Scenes
Catalyst: What do you
think happened at this crime
scene?
Today’s Agenda
• Review of principles from Blood Spatter Height Lab
• Different Blood Spatter Patterns
• Prep for the Fling Lab tomorrow (Last 15 minutes.. regardless of how far we get in the notes.)
Blood Spatter & Crime Scenes
The following notes are long, extensive, and gruesome. To get the MOST out of today’s lecture, do not copy everything you
see. For each scenario, make sure you have the following information: (1) relative size of blood, (2) relative shape of
blood, (3) possible cause of pattern, (4) any other interesting & relevant information.
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
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
Effect of Target SurfaceEffect of Target Surface
. .... .Spreads out smoothly ST of spreading edge is
broken by irregular surface
11
Wave Cast-offWave Cast-offDavid Sadler:David Sadler:
.Parent drop
wave cast-off
Tail of wave cast-off points back to parent drop
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 BloodspotsTracing Origin of Bloodspots
• 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)
• Medium velocity (25 - 100 f/s, 7.5 - 30 m/s)
• High velocity (>100 f/s, 30 m/s)
20
21
Low Velocity Blood SpatterLow Velocity Blood Spatter• Blood source subjected to LV impact
– < 5 f/s (1.5 m/s)
• Spot diameter: mostly 4 - 8 mm – some smaller, some larger
• Free-falling drops (gravity only)• Cast off• Dripping• Splashing• Arterial spurting
22
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
.... ...
..
...
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 PatternSplash Pattern
• Volume > 1 ml – Subjected to LV impact – Thrown – Tipped
• Large central irregular area surrounded by elongated peripheral spatter pattern
41
Splash 1Splash 1
5 ml blood squirted from a syringe from a height of 1 m
42
Splash 2Splash 2
5 ml blood squirted from a syringe from a height of 1 m
43
Splash 3Splash 3
5 ml blood squirted from a syringe from a height of 1 m44
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
• Blood source subjected to MV impact– (25 - 100 f/s, 7.5 - 30 m/s)
• Spot diameter: mostly 1 - 4 mm
54
Medium velocity blood spatter.Point of impact 15 cm in front of vertical target surface
6” ruler
55
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
71
Flow pattern72
Trapped!
73
Stabbing 1
74
Stabbing 275
Blood flow on shirt
Horizontally to R side
76
Pattern on shirt77
Bloodspots on trousers78
Fling Lab Pre-LabPurpose: To determine different characteristics of blood spatter patterns when using different weapons and different swing patterns.
Setup: 8 groups total: 4 groups will be testing different swing patterns; 4 groups will be testing different weapon types.
What needs to be done by tomorrow before the lab begins:1.Procedures written for how you are doing your test.2.Hypothesis about what you and your group expect to happen (and why).3.YOU NEED TO BRING GARBAGE BAGS THAT YOU CAN WEAR.
Blood Spatter Impact Angle Lab
http://www.nfstc.org/links/animations/images/blood%20spatters.swf
Blood Spatter Impact Angle Lab
1. Measure the length and width of the splatter.
2. Divide the width of the splatter by its length.
3. Determine the arcsin of that number, typically using a calculator with an arcsin function.
Blood Spatter Impact Angle Lab
1. Measure the length and width of the splatter.
2. Divide the width of the splatter by its length.
3. Determine the arcsin of that number, typically using a calculator with an arcsin function. (or p.523 in book)
Blood Spatter Impact Angle Lab1. Measure the length and width of the splatter.
2. Divide the width of the splatter by its length.
3. Determine the arcsin of that number, typically using a calculator with an arcsin function (or p.523 in book).
What impact angle did this blood drop hit?
Blood Spatter Impact Angle Lab1. Measure the length and width of the splatter.
2. Divide the width of the splatter by its length.
3. Determine the arcsin of that number, typically using a calculator with an arcsin function (or p.523 in book).
w/l = 1.5/3 = 0.5
Blood Spatter Impact Angle Lab1. Measure the length and width of the splatter.
2. Divide the width of the splatter by its length.
3. Determine the arcsin of that number, typically using a calculator with an arcsin function (or p.523 in book).
Arcsin(0.5) = 30º
Blood Spatter Impact Angle Lab
Pre-Lab:- Read through Lab 8-4 (p.229-233)- Draw the SETUP of one angle of your choice in your notebook.- Note that each group will be doing ALL angles- Find the angle of impact for the following blood drop dimensions:# Length (cm) Width (cm)
1 1 1
2 1.164 1
3 1.414 1
4 1 0.5735
5 6.253 1.3
The following are slides that will help with labs for later on.
Angle of Angle of ImpactImpact
90
10
70
2030
60 50 40
Adapted from Introduction to Forensic Sciences,W. Eckert, CRC, 1997
80
Gravitational dense zoneat lower edge
14
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
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
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
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