LECTURE #3 - Psychology and Police Investigations

how can ip assist the police with their activiites

• scientific approach

• research methods

• understand offenders and police

• attempts to develop practical strategies

why is crime linkage important

• pool evidence and resources

• obtain more severe sentences

different crime linkage scenarios (2)

• comparative case analysis

• crime linkage analysis

comparative case analysis

• large samples of crimes are searched by a practitioner for potential linkages

crime linkage analysis

• limited crimes are brought to a practitioner; needs to know whether crimes are linked

linking assumptions (2)

• behavioural stability

• behavioural distinctiveness

behavioural stability

• offenders will display similar behaviour across their crimes ( to some degree )

behavioural distinctiveness

• offenders commiting similar crimes will commit those crimes in a distinctive fashion ( to some degree )

C.A.P.D

• cognitive affective personality system

• personality traits and situational factors influence our behaviour

• behavioural strategies activated by internal fantasy

• strategy will be consistent

modus operandi

• method used by an offender to successfully commit a crime and get away with it

• assumes offenders will exhibit the same behaviours

challenges with MO

• mo is now always stable

• offender’s may chamge

behavioural signatures

• behaviour exhibited

• not necessary for crime commission

• satisfy some psychologial/emotional need

linkage databases

• capture info related to crimes committed across jurisdictions

• specially trained analysts attempt to identify linkages

challenges with databases

• data reliability and accuracy

• consistency and distinctiveness of MO and signatures

• ability of analysts to identify potential linkages

linkage as a diagnostic task

• two alternatives (yes-no)

  • discriminate between linked/unlinked crimes

  • evidence is available to assist with the task

  • ambiguous

  • must decide which evidence to use

diagnostic outcomes

• hit

• miss

• false alarm

• correct rejection

unambiguous

• occurs only for linked crimes or unlinked crimes

defining useful evidence

• degree of overlap can be measured using ROC

  • plots hit and false alarm rates as a function of threshold

measuring linkage accuracy

• measured as the auc

• higher the auc, the better the evidence is for linking

how good are we at linking crimes

• hard to tell

• studies used different measures of linking accuracy

what behaviours are most useful for linkage purposes

• those determined by the offender

what behaviours

• where and when offenders commit their crimes

is it easier to link certain types of crimes

• linking accuracy is higher for interpersonal crimes

are people good at linking crimes

• linking crimes is difficult

why is profiling important

• prioritise suspects

two assumptions underlying the profiling task

• behavioural stability

• homology

homology

• two crimes committed in a similar way, offenders may have similar background characteristics

latent traits

• assumed to be driving force behind behaviours exhibited in criminal and non-criminal contexts

organized-disorganized model

• crime scenes will vary from organized to disorganized

• backgrounds will vary from ‘‘

• organized crimes→ organized offenders;disorganized crimes → disorganized offenders

profile approaches

• deductive

• inductive

deductive profiling

• profiling background characteristics

• based onn evidence left at crime scenes

inductive profling

• profiling characteristics

• based on what we know about other offenders

IP approach to profiling

• determine if structure exists in the way offenders commit crime & in their background characteristics

• identify relationships between actions

are existing profile models valid

• models have been used without evidence of their validity

are profiling assumptions supported

• some evidence for stability assumptions

• no strong evidence for homology

do police think profiling is useful

• short answers: yes

biggest problem with research

• ecological validity