Testing the Effectiveness of Geo-

Behavioural Profiling Systems

Professor David Canter

&

Laura HammondDirector, Centre for Investigative Psychology

The University of Liverpool,UK

www.i-psy.com

Study of effectiveness of various prioritisation

strategies

92 offence series

in a London borough.

All identified series

over four years/

Various Models Illustrated from the crimes of Jack the

Ripper

The ‘canonical’ map

Nichols 31.8 –3.40Chapman 8.9 – 6.00

Stride 30.9 – 1.00Eddowes 30.9 – 1.45

Kelly 9.11- 7.00?

The ‘canonical’ map

Circle Hypothesis Calculation to Locate Ripper’s Base

Central Circle in Whitechapel

Centre of Gravity of Murder Locations

Two further concepts

Criminal Range Decay Functions

Criminal ‘range’

0-0.10.11-0.5

0.51-0.991.00-1.5

1.51-2.002.01-2.5

2.51-33.01-4

4.01-55.01-6

6.01-77.01-8

10+

0

5

10

15

20

25

30

35

Range of Distances traveled by Arsonists

The Distance Decay Function,An example from serial arsonists

Optimal Function of Distance from Offence to ‘Home’

Offence Map:

Developing the Search Tool that incorporates various distance functions.

1st Crime2nd

3rd

4th

5th

The system assigns a priority to each known offender using

various criteria.

Offender ID Address ProbabilityMO Match

124 Location A 0.28574311864 0

427 Location B 0.27038233898 0

427 Location C 0.26035169492 0

226 Location D 0.25577861017 0

48 Location E 0.23282991525 0

124 Location F 0.22445984746 0.3

124 Location G 0.21932662712 0

Prioritised search area

50% of actual offenders are in the top 5 prioritized just by geographical location. iOPS allows this to be improved by also using M.O. matching.

Criteria

• Distance from centre of circle defined by 2 furthest crimes

• Distance from centre of gravity (centroid)

• Optimum negative log decay function

• Negative log decay function with buffer

(N = 92)

Model Mean Rank (S.D) Median Rank

Exponential Function - High B-value 8.86 (8.446) 4

Logarithmic Function -Low B-value 9.04 (8.402) 4.5

Logarithmic Function -High B-value 8.92 (8.350) 5

Centre of Gravity 9.21 (8.256) 5

Logarithmic Function -Optimal B-value 8.95 (8.349) 5

Logarithmic Function with Buffer Zone- Optimal B-value 9.73 (8.674) 5.5

Exponential Function - Low B-value 10.18 (8.411) 7

Exponential Function - Optimal B-value 10.55 (8.461) 7

Exponential Function with Buffer Zone- Optimal B-value 10.61 (8.888) 7

Last Offence 11.11 (8.416) 9

First Offence 11.96 (8.424) 10..5

Centre of Minimum Distance 12.52 (8.066) 14

Centre of Circle 15.15 (7.536) 21

Straight Linear Function 21.00 ( .000) 21

COMPARISON OF 15 DIFFERENT MODELS

Need for more context specific examination of crime patterns

Taking account of Land use Opportunities for crime Guardianship Targeting Transport routes Temporal sequences

Offender 1:

34 CRIMES

1 HOME LOCATION

Offender

34 crimes

1 home location

Offender 2:

34 CRIMES

1 HOME LOCATION

Offender 34 crimes1 home location

2 Offenders with different distributions of crimse in relation to Southside Centre in Wandsworth

Southside Centre

Offender

34 crimes

1 home location

Offender 34 crimes1 home location

EXAMPLES FROM BURLGARIES IN WANDSWORTHPNC data

12 offenders

All crime types

1992-present

Offender 1:

10 CRIMES

2 HOME LOCATIONS

Offender 8:

24 CRIMES

1 HOME LOCATION

Offender 3:

20 CRIMES

3 HOME LOCATIONS

Offender 2:

21 CRIMES

3 HOME LOCATIONS

Offender 7:

13 CRIMES

2 HOME LOCATIONS

Offender 5:

19 CRIMES

3 HOME LOCATIONS

Offender 11:

48 CRIMES

3 HOME LOCATIONS

Offender 12:

53 CRIMES

2 HOME LOCATIONS