Toward Automatic Blood Spatter Analysis in Crime Scenes Gabriel Brostow, 13 June, 2006 Shen, Brostow, Cipolla University 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
Contact Gabriel J. Brostow or Amy Shen University of Cambridge
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