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