# *************F***C"***********"**************M"**N"**O"**P"**Q"**R

Testing the Effectiveness of Geo-

Behavioural Profiling Systems

Professor David Canter

&

Laura Hammond

Director, 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/

### Ripper

The ‘canonical’ map

Chapman 8.9 – 6.00

Nichols 31.8 –3.40

Kelly 9.11- 7.00?

Stride 30.9 – 1.00

Eddowes 30.9 – 1.45

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’

The Distance Decay Function,

An example from serial arsonists

25

20

35

30

15

10

5

0

0-0.1

0.51-0.99

0.11-0.5

1.51-2.00

1.00-1.5

2.01-2.5

2.51-3

3.01-4

4.01-5

5.01-6

6.01-7

7.01-8

10+

Range of Distances traveled by Arsonists

Optimal Function of Distance from Offence to ‘Home’

Offence Map:

Developing the Search Tool that incorporates various distance functions.

1st Crime

2nd

4th

3rd

5th

The system assigns a priority to each known offender using various criteria.

Prioritised search area

226

48

124

124

Offender ID

124

427

427

Location A

Location B

Location C

Location D

Location E

Location F

Location G

Probability

0.28574311864

0.27038233898

0.26035169492

0.25577861017

0.23282991525

0.22445984746

0.21932662712

0

0

0.3

0

0

0

MO

Match

0

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

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.

(N = 92)

COMPARISON OF 15 DIFFERENT MODELS

Model Mean Rank (S.D) Median

Rank

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

Logarithmic Function -Low B-value 9.04 (8.402)

Logarithmic Function -High B-value

Centre of Gravity

8.92 (8.350)

9.21 (8.256)

Logarithmic Function -Optimal B-value 8.95 (8.349)

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

Exponential Function - Low B-value 10.18 (8.411)

4.5

5

5

5

5.5

7

Exponential Function - Optimal B-value 10.55 (8.461)

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

Last Offence 11.11 (8.416)

7

7

9

11.96 (8.424) 10..5

First Offence

Centre of Minimum Distance 12.52 (8.066) 14

Centre of Circle 15.15 (7.536) 21

Straight Linear Function 21.00 ( .000) 21

Need for more context specific examination of crime patterns

Taking account of

 Land use

 Opportunities for crime

 Guardianship

 Targeting

 Transport routes

 Temporal sequences

Offender

34 crimes

1 home location

Offender 1:

34 CRIMES

1 HOME LOCATION

Offender 2:

34 CRIMES

1 HOME LOCATION

Offender

34 crimes

1 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 crimes

1 home location

EXAMPLES FROM BURLGARIES IN WANDSWORTH

PNC 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