The Use of Opportunity Structures in
Geographic Offender Profiling :
A Theoretical Analysis
Wim Bernasco
nscr.nl
What is Geographic Offender Profiling?
investigative technique
?
locations of a series of crimes
?
crimes committed by same offender
where is offender’s home?
?
Geographic Offender Profiling Tools
distance decay
Rigel (Rossmo)
Dragnet (Canter)
Predator (Godwin)
CrimeStat (Levine)
frequency
computer programs
distance
search priority map
How Geographic Profiling Tools Do
What They Do
Crime 1 Crime 2
Crime 3
street
Buffer Zones in Distance Decay
Crime 1 Crime 2
Crime 3
street
What GOP Tools Do Not Do
(Measure Opportunity)
Loc 1
Loc 2
?
Home 1
potential target location
actual target location
? possible offender home location
?
Home2
What GOP Tools Do Not Do
(Measure Attractiveness)
Home?1
?
Home2
attractive potential target location
potential target location
actual target location
? possible offender home location
Spatial Target Selection Model
(Bernasco & Nieuwbeerta, BJC 2005)
statistical model (conditional logit)
describes how offenders choose from a set of
alternative targets (target locations)
describes how they weight various features of potential
targets, including distance
assumes knowledge of alternatives and rationality
generalisation of distance decay model
can be reversed to serve as a GOP tool
Simulation Study
Aim
study the new GOP approach in a controlled environment
assess under which conditions the new GOP approach
could improve existing GOP tools
assess to what extent the new GOP approach could
improve existing GOP tools
Method
simulation of 5 target choices of 100 individual offenders on a
10 by 10 grid ‘island’ (opportunity space)
calculate priority map using the 5 linked crime locations
calculate GOP efficiency using search area index (Canter et
al., 2000)
Simulation: Opportunity Structures
target
no target
unclustered
targets (uniform)
weakly clustered
targets
strongly
clustered
targets
Simulation: Opportunity Structures
attractive target
regular target
no target
unclustered
targets,
attraction
clustered
weakly
clustered
targets,
attraction
clustered
strongly
clustered
targets,
attraction
clustered
All Six Opportunity Structures
attractivesness clustering
opportunity clustering
Simulation: 3 GOP tools
Tool A
does not measure opportunity
does not measure attractiveness
‘blind’
Tool B
measures opportunity
does not measure attractiveness
‘color blind’
Tool C
measures opportunity
measures attractiveness
‘20/20 vision’
Simulation: Results
Search Area Index (Smaller is Better)
attractivesness clustering
opportunity clustering
none
A
none B
C
A
strong B
C
12
12
12
32
30
18
weak
A
B
C
A
B
C
34
18
18
43
39
25
strong
A
B
C
A
B
C
46
28
28
48
43
33
Conclusions
measurement of spatial variation in opportunity
and attractiveness can improve GOP
improvement most marked where there is strong
clustering of targets and of target attractiveness
Discussion
method is easily extended to include
timing of offences (sequence number)
characteristics of unknown offender
measurement opportunity structures is costly
measurement attractiveness is difficult
empirical evidence is yet lacking
usefullness of GOP tools in general is challenged
laymen are just as good
real-life detectives may be even better