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Toward Automatic Blood Spatter Analysis in Crime Scenes

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

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Toward Automatic Blood Spatter Analysis in Crime Scenes

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

  2. 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

  3. Image by Kevin Maloney

  4. Point of Origin Localization

  5. String Method

  6. Support Software From BackTrack software by A. L. Carter, 2001 version

  7. Automation Goals • Estimate impact angles for 1 spot • Estimate 2D origin of impact • Estimate 3D origin of impact

  8. Automation Goals • Estimate impact angles for 1 spot • Estimate 2D origin of impact • Estimate 3D origin of impact

  9. Experimental Setup

  10. Results: Impact Angles

  11. Primary vs. Secondary Stains Bevel & Gardner, 2001

  12. Filter for Outliers

  13. Automation Goals • Estimate impact angles for 1 spot • Estimate 2D origin of impact • Estimate 3D origin of impact

  14. 2D Multi-Spot Analysis • Experiment • Blunt force impact • True origin: • diameter 6cm • height 22cm

  15. Strings in the form of vectors y x

  16. Intersections

  17. Convolve with Gaussian

  18. Threshold on Distance

  19. Image rectification • Generate synthetic view • Homography:

  20. Image rectification

  21. Automation Goals • Estimate impact angles for 1 spot • Estimate 2D origin of impact • Estimate 3D origin of impact

  22. Height Estimation • Triangulation • H = tan(a) * distance • True height 22cm, estimated height 19cm • Advanced • Unknowns • Speed, distance, air resistance and gravity

  23. Height Estimation • Triangulation • H = tan(a) * distance • True height 22cm, estimated height 19cm • Model in future • Speed, distance, air resistance and gravity

  24. Findings • Demonstrated accuracy of 1-spot analysis • 2D Origin of Impact Estimation • Overhead crime-scene visualization • Groundwork for 3D string method automation

  25. Future Work • Real blood images • 3D projectile trajectory modeling

  26. Contact Gabriel J. Brostow gjb47@cam.ac.uk or Amy Shen ars42@cam.ac.uk University of Cambridge

  27. 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

  28. Alternative bloodstain ellipse fitting • Alternative ellipse fitting algorithm • Ellipse growth • Erosion, median filter and dilation

  29. 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 Manual vs. Automatic

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