Файл: [D._Kim_Rossmo]_Geographic_Profiling(BookFi.org).pdf

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After the arrest of Wayne Williams, police were able to determine that

he had, in the past, done freelance photography assignments near several of
the victim’s burial sites. “Very few criminals appear to blaze trails into new,
unknown territories or situations in search of criminal opportunities”
(Brantingham & Brantingham, 1998, p. 4). This spatial selection process is
consistent with the routine activity approach with its emphasis on the rele-
vance of regular and routine victim behaviours for an understanding of crime
patterns (Clarke & Felson, 1993a). Ford (1990) stresses the investigative
importance of identifying “routine victim activities and expected behaviors
related to contact with and risk of victimization by a serial predator” (p. 116).

Crime pattern theory combines rational choice, routine activity theory,

and environmental principles to explain the distribution of crimes. Target
choice is affected by the interactions of offenders with their physical and
social environments (Brantingham & Brantingham, 1993b). Potential victims
are not considered in isolation from their surrounding environment; the
entire “target situation” must be seen as acceptable by the offender before a
crime will occur (Brantingham & Brantingham, 1993b).

“

Pattern

 is a term used to describe recognizable interconnectiveness

[physical or conceptual] of objects, processes, or ideas” (Brantingham &
Brantingham, 1993b, p. 264). This is a multidisciplinary approach that
explores patterns of crime and criminal behaviour through an analysis of the
processes associated with crime, site, situation, activity space, templates,
triggering events, and motivational potential.

“Each criminal event is an opportune cross-product of law, offender

motivation, and target characteristic arrayed on an environmental backcloth
at a particular point in space-time. Each element in the criminal event has
some historical trajectory shaped by past experience and future intention, by
the routine activities and rhythms of life, and by the constraints of the
environment” (Brantingham & Brantingham, 1993b, p. 259). Environment
in this context involves sociocultural, economic, institutional, and physical
structures, at micro, meso, and macrolevels.

Brantingham and Brantingham used the concepts of opportunity, moti-

vation, mobility, and perception in the development of their model of crime
site geography. The model is based upon the following propositions:

(1)Individuals exist who are motivated to commit specific offenses.

(a)The sources of motivation are diverse. Different etiological models or
theories may appropriately be invoked to explain the motivation of different
individuals or groups.

(b)The strength of such motivation varies.

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(c)The character of such motivation varies from affective to instrumental.

(2)Given the motivation of an individual to commit an offense, the actual
commission of an offense is the end result of a multistaged decision process
which seeks out and identifies, within the general environment, a target or
victim positioned in time and space.

(a)In the case of high affect motivation, the decision process will probably
involve a minimal number of stages.

(b)In the case of high instrumental motivation, the decision process locating
a target or victim may include many stages and much careful searching.

(3)The environment emits many signals, or cues, about its physical, spatial,
cultural, legal, and psychological characteristics.

(a)These cues can vary from generalized to detailed.

(4)An individual who is motivated to commit a crime uses cues (either
learned through experience or learned through social transmission) from
the environment to locate and identify targets or victims.

(5)As experiential knowledge grows, an individual who is motivated to
commit a crime learns which individual cues, clusters of cues, and sequences
of cues are associated with “good” victims or targets. These cues, cue clus-
ters, and cue sequences can be considered a template which is used in victim
or target selection. Potential victims or targets are compared to the template
and either rejected or accepted depending on the congruence.

(a)The process of template construction and the search process may be
consciously conducted, or these processes may occur in an unconscious,
cybernetic fashion so that the individual cannot articulate how they are
done.

(6)Once the template is established, it becomes relatively fixed and influ-
ences future search behavior, thereby becoming self-reinforcing.

(7)Because of the multiplicity of targets and victims, many potential crime
selection templates could be constructed. However, because the spatial and
temporal distribution of offenders, targets, and victims is not regular, but
clustered or patterned, and because human environmental perception has
some universal properties, individual templates have similarities which can
be identified. (1981, pp. 28–29)

.

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Targets are selected from an offender’s awareness space and assessed

against the criteria of suitability (gain or profit) and risk (probability of being
observed or apprehended). These targets are scanned for certain cues (visi-
bility, unusualness, symbolism) that are evaluated in terms of fit to the
individual’s template. From the perspective of the offender, rational choices
are then made and specific targets chosen for victimization. Such a selection-
process is consistent with the concept of an offender operating within his or
her “comfort zone” (Keppel, 1989).

A person’s awareness space forms part of his or her mental map and is

constructed primarily, but not exclusively, from the spatial experiences of the
individual. An awareness space is derived from, amongst other sources, an
activity space, the latter being composed of various activity sites (residence,
workplace, social activity locations, etc.) and the connecting network of travel
and commuting routes. Well-known locations (landmarks, tourist sites,
important buildings) may also become part of a person’s awareness space
without actually being a component of their activity space.

Brantingham and Brantingham propose a dynamic process of target

selection, with crimes occurring in those areas where suitable targets overlap
the offender’s awareness space (

Figure 7.2

). Offenders then search outward

from these areas, the search behaviour following some form of distance-decay
function (Brantingham & Brantingham, 1981, 1984; Rhodes & Conly, 1981).
Search pattern probabilities can be modeled by a Pareto function, starting
from the sites and routes that compose the activity space and then decreasing
as distance away from the activity space increases. The Pareto function,

Figure 7.2

    Crime site search geography.

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named after the Italian economist, is suitable for fitting data that have a
disproportionate number of cases close to the origin, making it appropriate
for modeling distance-decay processes (Brantingham & Brantingham, 1984).
It takes the general form: 

y

 = 

k

/

x

b

.

There is usually a “buffer zone,” however, centred around the criminal’s

residence, comparable to what Newton and Swoope (1987) call the coal-sack.
effect. Within this zone, targets are viewed as less desirable because of the
perceived level of risk associated with operating too close to home. For the
offender, this area represents an optimized balance between the maximization
of opportunity and the minimization of risk. The buffer zone is most appli-
cable to predatory crimes; for affective-motivated offences it takes on less
importance, as can be seen by the fact that domestic homicides usually occur
within the residence. 

Figure 7.3

 shows an example, derived from a serial rape

case, 

38

of a typical buffered distance-decay function. The radius of the buffer

zone is equivalent to the modal crime trip distance. 

When Canter and Larkin (1993) regressed maximum distance from

crime site to home against maximum distance between crime sites for a group
of serial rapists in England, they found a regression equation constant equiv-
alent to 0.98 kilometres (see Equation 6.5, above). This was the “safety zone”

Figure 7.3

    Distance-decay function.

38 

Figure 7.3

 displays the fourth-order polynomial trend line fitted (

R

2

 = 0.730) to 79 crime

trip distances for John Horace Oughton, the Vancouver Paperbag Rapist (Alston, 1994; see
also Eastham, 1989).

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within which sexual offenders are less likely to strike. Employing a similar
analysis, Canter and Hodge (1997) found such zones for both U.S. and British
serial killers (3.44 km and 0.53 km, respectively). But the idea of a “safety”
is misleading, and some studies have misinterpreted the buffer zone as rep-
resenting an area of no criminal activity. This is incorrect; a decrease in
probability is not the same as zero probability. Much depends on whether
an offender believes he or she can get away with the crime. Under the right
circumstances, rapists have been known to attack women who live in their
same apartment building.

There may be another explanation for the existence of the buffer zone.

As the distance from an offender’s residence increases, so do the number of
potential targets. The increase in criminal opportunity is linear; for example,
there are twice as many possible targets at a distance of two kilometres than
there are at one kilometre from an offender’s home. More generally, the target
ratio between two distances is:

t

2

/

t

1

 = 

d

2

/ 

d

1

(7.1)

where:

t

2

  is the number of potential targets at 

d

2

;

t

1

  is the number of potential targets at 

d

1

;

d

2

 is the second distance; and

d

1

 is the first distance.

Combining the linear increase in opportunity with the exponential

decrease in travel inclination creates a buffered distance-decay function. This
process is equivalent to a spiral search that may be a more accurate means
of describing what offenders really do. The search may be physical, or it may
be mental as various possible targets are considered and assessed (see Wright
& Decker, 1996). Modeling this process produces theoretical distributions
that closely match empirical ones. Mean and modal journey-to-crime dis-
tances can be varied through a parameter describing the probability of target
selection. Greater distances result from either specific limited targets or dis-
cerning offenders (i.e., lower target selection probabilities). This may explain
many of the empirical results found in the journey-to-crime literature.

The journey-to-crime function, comprised of least effort, spiral searches,

and detection avoidance, could be the result of something known as the
principle of least action. First suggested in 1744 by Pierre-Louis Maupertuis,
a Berlin scientist, and later developed by the famous French mathematician
Joseph-Louis Lagrange, least action refers to the minimization of quantities
within dynamic systems (e.g., energy, distance, time, change, effort, cost,
etc.). Most aspects of nature seem to follow the rule of economy suggested
by the least action principle. It appears in theoretical physics, linguistics,