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Blood Spatter Analysis
Presented by
Patricia Nolan Bertino
Bud Bertino
Blood Spatter (not splatter)
is the pattern of blood created when blood is deposited on a surface.
Bloodstain EvidenceBloodstain EvidenceMay 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
Liquid BloodLiquid Blood• Physical properties
– viscosity– surface tension– specific gravity
• Behaves as a projectile in motion– biology, physics, maths
2
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
____________ bleeding does not result in smaller drops.
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
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
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 Shape & Size of BloodspotBloodspot
• 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
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
Angle Angle of 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
Wave Cast-offWave Cast-offDavid Sadler:David Sadler:
.Parent drop
wave cast-off
____________________________________________
__________________________________________
15
Types of Injury
• High velocity (gunshot)
• Medium velocity (hammer strike)
• Low velocity ( drip)
Characteristics of a single drop of blood
Spike vs. satellite
Surface variations
Rough tile unvarnished wood
Smooth (glass)
Slightly raised
floor tiling varnished wood, fabric
Blood dropped from different heights
Review: Blood spatter “tells a story”
• Where was person located when bleeding?
• What direction was blood traveling?
• What was the angle of impact?
• Analyze crime scene p21