Forensic Psychology For Dummies (61 page)
Read Forensic Psychology For Dummies Online
Authors: David Canter
So, although certain unusual behaviours of an offender can sometimes be used to help characterise his actions (and may then be called his M.O.), he may not always do them. Hence I leave the term ‘M.O.’ to the amateur sleuths and I stick with exploring a criminal’s actions.
In order to help in the criminal investigative cycle, psychologists need to have a full understanding of the sorts of things that detectives need to know that various psychological sources can answer (see Table 6-1).
Table 6-1 The Questions That Detectives Need Answering
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Profiling equations
The inferences that make up ‘offender profiles’ can be thought of as rather like mathematical equations that link the ‘Actions’ in a crime to ‘Characteristics’ of the offenders. So I call them A → C equations. The → here implies that there may be any of a number of relationships between actions and characteristics. The mythbuster gives more detail. One important aspect of investigative psychology is trying to unravel these equations to come up with useful inferences.
It’s rare for one simple aspect of a crime to imply one simple characteristic of the offender. The ‘clue’ so favoured by fiction writers that opens the way to the offender (such as a suspect using the word ‘cell’ for his ‘mobile phone’ showing he lived in the US where that term is the usual one) may come from forensic evidence such as fibres and body fluids, but when dealing with criminal actions it’s usually the pattern of actions that points the way, not one specific action.
Actions
in the profiling equations mean all the information about the crime that the police have before they know who did it: for example, the place and time of the offence, as well as the details of the victim and what actually happened.
in the profiling equations mean all the information that’s of use to the police in solving the crime, such as where the offender may be living or what other crimes he has been convicted of that’ll be recorded in police databases.
Inferring isn’t an exact science
In one rape case I worked on, the victim reported that the offender had long fingernails on his right hand but short ones on his left hand. Detectives became excited when they remembered that some guitar players keep their nails like this. So were we looking for a sexually violent guitarist? No. When he was caught, police found that he had no musical talents at all, but in fact worked replacing tyres on cars, which seemed to result in him wearing down the nails on one hand more than on the other.
Unfortunately, no necessary simple equation exists in which one Action can always be used reliably to infer one Characteristic. The anecdote in the nearby sidebar ‘Inferring isn’t an exact science’ illustrates this point. Sometimes combinations of Actions offer the possibility of the various likely Characteristics. So possessing a firearm and using it with accuracy and confidence, for example, may imply that a person’s a firearm enthusiast or that he’s had military training.
Facing the challenge of contingencies
Contingencies
are those aspects of the circumstances in which a crime occurs that can influence what inferences can be made about that crime. So any investigative psychologist trying to derive inferences needs to take account of these. The following aspects challenge the possibility of developing a simple ‘profiling’ equation (see the preceding section):