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Toward Automatic Blood Spatter Analysis in Crime
Scenes
Gabriel Brostow, 13 June, 2006
Shen, Brostow, CipollaUniversity of Cambridge
Bloodstain Categories*
• Passive Bloodstains
• Projected Bloodstains– Low / medium / high velocity impact:
caused by force applied to a blood source
• Transfer/Contact Bloodstains
*International Association of Bloodstain Pattern Analysts
Image by Kevin Maloney
Point of Origin Localization
String Method
Support Software
From BackTrack software by A. L. Carter, 2001 version
Automation Goals
1. Estimate impact angles for 1 spot
2. Estimate 2D origin of impact
3. Estimate 3D origin of impact
Automation Goals
1. Estimate impact angles for 1 spot
2. Estimate 2D origin of impact
3. Estimate 3D origin of impact
Experimental Setup
Results: Impact Angles
Primary vs. Secondary Stains
Bevel & Gardner, 2001
Filter for Outliers
Automation Goals
1. Estimate impact angles for 1 spot
2. Estimate 2D origin of impact
3. Estimate 3D origin of impact
2D Multi-Spot Analysis
• Experiment– Blunt force impact– True origin:
• diameter 6cm• height 22cm
Strings in the form of vectors
x
y
Intersections
Convolve with Gaussian
Threshold on Distance
Image rectification
• Generate synthetic view
• Homography:
Image rectification
Automation Goals
1. Estimate impact angles for 1 spot
2. Estimate 2D origin of impact
3. Estimate 3D origin of impact
Height Estimation
• Triangulation– H = tan() * distance– True height 22cm,
estimated height 19cm
• Advanced– Unknowns– Speed, distance, air
resistance and gravity
Height Estimation
• Triangulation– H = tan() * distance– True height 22cm,
estimated height 19cm
• Model in future– Speed, distance, air
resistance and gravity
Findings
• Demonstrated accuracy of 1-spot analysis
• 2D Origin of Impact Estimation
• Overhead crime-scene visualization
• Groundwork for 3D string method automation
Future Work
• Real blood images
• 3D projectile trajectory modeling
Related work
• Interpretation of Bloodstain Evidence at Crime Scenes – Eckert & James, 1998
• Bloodstain Pattern Analysis– Bevel & Gardner, 2001
• Blood Dynamics– Wonder, 2001
• The Directional Analysis of Bloodstain Patterns, Theory and Experimental Validation– A.L.Carter, 2001
Alternative bloodstain ellipse fitting
• Alternative ellipse fitting algorithm– Ellipse growth– Erosion, median filter
and dilation
Manual vs. Automatic
• Current pipeline:– On-site measurements– Physical strings
construction– Qualitative estimation
of origin
• Automatic pipeline:– Image processing– Strings in the form of
equations stored on computer
– Quantitative estimation of origin using error functions
