Director’s
Message
DNA
Analysis for “Minor” Crimes: A Major Benefit for Law
Enforcement
Tracking
Prisoners in Jail With Biometrics: An Experiment in a Navy Brig
Predicting
a Criminal’s Journey to Crime
Victim
Satisfaction With the Criminal Justice System
Police Responses to Officer-Involved Shootings
Automated Information Sharing: Does It Help Law Enforcement Officers
Work Better?
NIJ
and Harvard University Host Webcasts on Less Lethal Force and DNA
in “Minor” Crimes
Books in Brief
Publications of Interest From NIJ
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NIJ
Journal No. 253 January 2006
Predicting a Criminal’s Journey to Crime
Phil Canter sits at his computer desk at the Baltimore
County Police Department’s main office in Towson,
Maryland. Canter calls up the menu for CrimeStat, a computer
program that helps police organize data and analyze crime
patterns. Canter makes a selection from the program, then
calls up Regional Crime Analysis Geographic Information
System (RCAGIS), another crime-fighting computer program.
Soon, a detailed street map of Baltimore County appears
on the computer screen. With a few more keystrokes, Canter
zooms in on one part of the county. Next, he pulls up a
list of all sexually related home burglaries that have been
reported in that area within the past 6 months. With a few
more keystrokes, Canter locates the precise sites of each
reported crime on the map, along with the area’s buildings,
waterways, and other manmade and natural features. Then
he adds a list of known sexual offenders, separates them
by method of operation, and keys in their last known addresses.
Eventually, a list of possible suspects is generated.
Location: The Key to Solving Crimes?
The utility of these computer programs as crime-solving
tools is promising. “We can use computer programs
to analyze crime patterns and depict geographically where
certain crimes are clustered, relate those crimes to the
environment in which they occur, and identify where the
potential suspects most likely live,” says Canter,
chief statistician for the Baltimore County Police Department.
“That’s as important [to solving crimes] as
a suspect’s description. It helps police understand
better the areas where crimes occur. And it lets them focus
on suspects with the highest probability of [having committed]
the crime.”
In recent years, several police departments have added
computer programs to their arsenal of anti-crime tools.
Although still an imprecise science, computer programs have
been or are being developed that can help police locate
crime “hot spots,” spatially relate a list of
potential suspects to actual crimes, profile crimes geographically
to identify where a serial criminal most likely lives, and
even forecast where the next crime in a series might occur.
One of the oldest approaches to using computers to analyze
crime patterns is known as geographic profiling. Developed
in the late 1980’s, geographic profiling involves
the use of computer models to spatially analyze crime sites
so that investigators can determine the most likely areas
where an offender lives. “Geographic profiling assigns
probability values to particular geographic areas,”
says D. Kim Rossmo, a research professor at Texas State
University in San Marcos who helped develop the model. “It
tells police where to look first.”
Geographic profiling is most useful, Rossmo says, in cases
where the same person or group of persons has committed
a number of crimes such as murders, sexual assaults, robberies,
bombings, or arsons. It is particularly helpful when offenders
commit crimes at different sites, where two crimes are committed
at once (such as a rape in which the victim’s purse
is also stolen), or in cases where an assault or theft victim’s
credit card is subsequently used at various locations.
In undertaking geographic profiling, Rossmo and other trained
profilers typically review the case files and talk to police
investigators to make sure that the case is an appropriate
one for this specific approach. Next, profilers tour the
crime sites to visualize what happened and see if anything
was missed. Then they run the information through Rigel™,
a computer software package that analyzes crime sites. The
profiling process, which includes preparation of a written
report identifying the most probable areas where an offender
might live, usually takes about 2 weeks, he says. As a result,
most profilers are only able to complete about 20 cases
a year. As a practical matter, that limits opportunity to
use geographic profiling to cases of local or national significance.
CrimeStat: Hitting Home
CrimeStat, one of the models used by Baltimore County’s
Canter, is a stand-alone spatial statistics program for
the analysis of crime incident locations. Developed under
grants from NIJ to Ned Levine and Associates, CrimeStat
III Software is free and can be downloaded from the Internet
at http://www.icpsr.umich.edu/CrimeStat/.[1]
The program makes use of data derived from geographical
information systems (GIS), which combine digital, computer-generated
maps with data that can be displayed and manipulated. CrimeStat
includes a component known as the journey-to-crime module,
which is one aspect of the multifaceted geographic profiling
technology.
CrimeStat builds on one simple concept: criminals have
to start from somewhere when they set out to commit a crime.
On the basis of the location of incidents committed by the
serial offender, the journey-to-crime module makes statistical
guesses about where the criminal is likely to reside. Those
guesses are based on the travel patterns of a sample of
known serial offenders who committed the same type of crime.
Based on the theory that most crimes are committed close
to an offender’s home, the module estimates the distance
serial offenders travel to commit crimes and, by implication,
the likely location from which they begin their “journey
to crime.”
The presumption underlying this analysis is that offenders,
when confronted with more than one possible location for
committing a burglary, will select the one with the greatest
potential payoff and the least travel time. This pattern
may vary, however, by type of crime. For example, although
most rapes, burglaries, assaults, and other crimes of opportunity
fit this pattern, more deliberative crimes—like auto
thefts and commercial robberies—may occur farther
from home, maximizing the offender’s potential reward
and decreasing his or her risk of being recognized. By plotting
the location of crimes committed by a serial offender and
then using a model of travel distance to estimate the offender’s
likely area of origin, the program attempts to lead law
enforcement officers to the offender’s own neighborhood.
But Do They Really Work?
Beyond serving as research projects and interesting toys
for crime analysts, the key question remains: Do sophisticated
computer programs work? The answer isn’t a simple
“yes” or “no.”
Daniel Helms, a crime analyst with the National Law Enforcement
and Corrections Technology Center (NLECTC) in Denver, believes
they do. Computer models “are not a magic bullet,
but they are powerful tools [that] give police a better
starting place for following up leads and checking out lists
of known offenders,” he says.
To illustrate his point, Helms cites the case of the Las
Vegas, Nevada, police who used CrimeStat and other computer
models to identify a probable area where a serial killer
lived. Based on that information, police canvassed a large
apartment complex in that area and questioned residents
if they had seen anyone who matched the description of the
killer. Normally, the police might have overlooked that
apartment complex because it was not the residence of any
known suspect; however, because of the information provided
by CrimeStat, they staked out the complex and ultimately
arrested a suspect. In this case, CrimeStat gave police
an “insight into crime and criminals not available
before,” Helms says.
The case of the “blue bandana bandit” in Glendale,
Arizona, is another example of the value of computer models
in solving crimes. In this case, police knew that a suspect
wearing a blue bandana had committed a series of robberies
at a chain of convenience stores. Glendale crime analysts
and police detectives used a geographic information system
to plot where the robberies had occurred and then used CrimeStat
to predict where the next one might take place. Police staked
out that convenience store and made an arrest.
Critics Weigh In
But not all crime analysts are convinced that geographic
profiling and other computer models work that well. Richard
Block, a professor of sociology and criminal justice at
Loyola University in Chicago who works on CrimeStat and
other computer models, questions their utility. “[Computer
models] have not been adequately tested to know whether
they will work better than a detective’s intuition,”
he observes. “This is a very new field that is still
being developed.”
The belief that no computer model, however effective, will
eliminate the need for good old-fashioned police work is
shared by critics and proponents alike. “Police still
need to use their own intuition and other information when
investigating crimes,” Phil Canter acknowledges. “Computer
models supplement what detectives find on their own. They
can provide insights into the travel patterns of criminals,
but we should not take them as gospel.”
Effectiveness Depends on Law Enforcement Input, Acceptance
A related problem, Canter notes, is that CrimeStat and
other computer programs depend on the accuracy and thoroughness
of the information obtained by law enforcement officers.
Sometimes the most basic GIS data are incorrect, especially
the addresses of known offenders and other suspects. Too
often, notes Brian Hill, a police department crime analyst
in Glendale, Arizona, officers have to rely on self-reported
data from unreliable witnesses and suspects.
Additionally, many police officers are not familiar or
experienced enough with sophisticated computer programs
to use CrimeStat and other programs effectively. Using these
programs requires training as well as an ability to understand
technical manuals and interpret statistical results. “You
can’t just plug in the computer and start the program,”
NLECTC’s Helms adds. “You have to understand
how it works.”
Origins of Journey May Vary
More importantly, offenders may not always start their
journey to crime from home, says Derek Paulsen, assistant
professor of criminal justice at Eastern Kentucky University
in Richmond. In some cases, criminals may start from their
workplace, or a friend’s or relative’s home.
Alternatively, the journey may start from a spot where the
individual hangs out—which may also be the place where
he or she purchases drugs. And because criminals tend to
move so often, an address that is correct one day may be
out of date the next. These variables directly impede analysts’
abilities to identify a criminal’s journey to crime.
Applying this theory is more complicated than drawing a
straight line from a suspect’s home to a crime site.
Moreover, today’s mobile society makes predicting
where offenders started their journey to crime based on
known crime sites very difficult. Take, for example, the
case of the snipers who launched a series of random shootings
in 2002 that terrorized Washington, DC, and its suburbs,
killing 10 people and wounding another 3. Despite using
geographic profiling and other computer models in one of
the most intense police manhunts in U.S. criminal history,
the suspects were identified based on clues provided by
one of the snipers about a seemingly unrelated case in Alabama.
Moreover, despite implementation of a massive law enforcement
dragnet for the two suspects, they were ultimately caught
after an alert motorist saw them sleeping in their car—50
miles from the closest crime scene.
The sniper case also illustrates the limits of any computer
program to adequately analyze the complexity of human behavior,
says Ronald Wilson, program manager of the Mapping and Analysis
for Public Safety (MAPS) program at NIJ. “There is
a lot in human behavior that cannot be accounted for by
mathematical models,” Wilson notes, pointing to the
more intelligent criminals who deliberately try to vary
their methods of operation to confuse or foil police.
Looking Into the Future
How long will it take before sufficient research and testing
have been completed and CrimeStat and other computer programs
can be recommended for use by police departments? Loyola
University’s Block predicts they may be sufficiently
accurate and reliable to use in a year or two. “They
have a lot of promise,” he says. “They are a
potentially very useful tool in solving crimes.”
In the end, however, no single police technique will work
every time for every case. In some cases, computer programs
may provide the key to solving crimes; in others, however,
traditional police work will make the difference. “If
we can better understand crime as a series of trips in time,
space, and distance,” observes Ned Levine, “maybe
we can begin to predict where crimes will be committed and
where the offenders came from.” To accomplish this
goal, however, more complex and realistic computer programs
must be developed.
NCJ 212264
Note
- For additional information on crime mapping and related
software, consult NIJ’s MAPS (Mapping and Analysis
for Public Safety) program at http://www.nij.gov/topiocs/technology/maps.
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