toward automatic blood spatter analysis in crime scenes

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

Contact

Gabriel J. Brostowgjb47@cam.ac.uk

or

Amy Shenars42@cam.ac.uk

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