forensic psychology top down bottom up

Offender profiling

Investigators look at observable details of a crime scene and use these to make assumptions about the person who commited the crime

top down approach

The FBI interviewed 36 murderers and, based on characteristics of their crimes, created two categories: organised and disorganised

If a crime scene matches some characteristics of one category, we can predict other likely characteristics of the offender.

organised offenders

evidence of planning the crime - victim deliberatly targeted. killer may have type of victim

little evidence left and high degree of control

above average iq - in skilled profession

usually married with children

disorganised offenders

little evidence of planning - crime may have been spontatneous

crime scene shows it was impuslive

below average iq - unskilled work or unemployed

history of failed relationships, living alone and sexual dysfunction

4 main stages of construction of fbi profile

data assimilation - review of evidence (photos, reports ect)

crime scene classification - organised or disorganised

crime reconstruction - generate hypotheses about behaviour and events

profile generation - generation of hypotheses about the offender.

limitations of top down approach

all interviews that fbi conducted were americans convicted of sexually motivated murders. meaning findings may not genralise to other types of crime or criminal.

small sample size - only 36 murderers therefore may not generalise to all criminals.

interviews were not structured or standardised. this is because they reviewed interviews that already took place. so process may lack objectivity.

bottom up approach

A method where profiles are built by analysing crime scene evidence and identifying patterns, rather than using pre-set categories. It is data-driven (starts with evidence) rather than theory-driven and does not use fixed offender types like organised/disorganised.

investigative psychology

A bottom-up method that looks for patterns in behaviour and uses statistics to link crimes and build offender profiles.

geographical profiling

when investigators use information from crime scenes to predict where an offender lives. canters technique is to plot all of the offenders crime locations on a map. and use them to draw a circle. he likely lives in the circle. A marauder operates close to home, while a commuter travels away from their home area to offend.

john duffy case study

commited series of sexual assault and rapes mostly in north london which took place near a rail way station. over several years duffy attacked dozons of women and murdered three. Canter made 17 predictions about duffs profile and 13 of these turned out to be correct.

Canter and Lundrigan’s 2001 study supports Canter’s predictions about geographical profiling.

found that most serieal killers disposed of victim bodies within 15 kilometers of their home. this supports the idea that criminials priortise locations that are familiar to them. Then as an offender gets more experience and confidence they start to operate in locations that are furhter and further away. finally despite gradual increase the anaylsis picked out out a clear domain for each offender. supporting the idea that geographical data can differentiate between offenders

strength of bottom up: research support.

The bottom-up approach has research support

David Canter analysed 100 murder cases and identified consistent behavioural patterns.

This suggests offender behaviour can be understood through statistical patterns rather than fixed categories.

Therefore, the bottom-up approach is supported by evidence and has scientific credibility.

strength of bottom up : scientific

The bottom-up approach is more scientific than the top-down approach.

It uses objective data analysis and statistical techniques from crime scenes.

This reduces reliance on intuition and subjective judgement by investigators.

Therefore, it produces more reliable and evidence-based offender profiles.

limitation: geographical profiling limited usefulness

Geographical profiling has limited usefulness.

It only works when crimes are part of a series.

This means it cannot be applied to one-off offences

Therefore, part of the bottom-up approach has restricted practical application