Canter (1995, 2000) in the original sketching of the A🡢C equation, makes the key point that for offender profiling to operate, it needs to assess the salience of the variables that are employed for the crime scene classification process.
- IP began with a focus on salience and identifying the crime scene actions that best distinguish behavioural subtypes.
A sexual crime's sexual element or a homicide's victim's death would be present in most crime scenes.
- Certain crime scenes exhibit highly individualised behaviours that are not suitable for a model that attempts to summarise crime scene characteristics.
- To identify one crime from another, the most significant crime scene characteristics must be identified to classify crime scenes into subtypes with similar traits.
- Each crime scene subtype has its own characteristics, yet their activities will have a psychological connection.
- This gives a framework for comparing and classifying crime scenes based on evidence.

The first IP homicide model, which followed IP principles of information retrieval and analysis of criminal behaviour from case files, connected activities within each subtype and differentiated crime scene subtypes (see Salfati & Canter, 1999). This model identified these subtypes:
- Expressive-Impulsive
- This type of homicide involves a series of erratic and impulsive actions against a victim with personal importance in an emotionally charged situation.
- These homicides are often impulsive because the culprit utilises a weapon found at the spot or brings one, emphasising a violent encounter.
- These killers often have a history of impulsive and violent crimes, which shows how they have behaved with others in the past and how they handle conflict in general.
- Instrumental-Opportunistic
- This type of homicide targets vulnerable victims of opportunity used as conduits. Strangulation, kicking, and punching injure the victim.
- In certain cases, the perpetrator steals goods and/or sexually assaults the victim.
- These offenders tend to commit robbery and burglary rather than theft.
- Instrumental-Cognitive
- This category of homicide has a cognitive emphasis, victims are objectified, the offender keeps calm throughout and after the crime, and they strive to remove forensic evidence, transport the body, or dispose of the body.
- These behaviours show that the perpetrators are purposefully distancing themselves from the victim and crime, therefore removing themselves as suspects. These crooks know forensic evidence.
- These cognitive crimes are committed by experienced criminals who have served time in prison.
Developing crime scene subtype categorization and differentiation models requires identifying the strongest psychological themes.
- Psychological patterns or themes of crime scene behaviour are more important than individual behaviours.
Intelligence Penetration (IP): This is a branch of study that seeks to categorise criminal conduct into separate subtypes whose behaviours share common psychological elements.
- This technique to classification and individual distinction is fundamental to behavioural analysis in IP and serves as the foundation for all research in the discipline.
Early studies produced categorization methods and instructed law enforcement officials to use them, but did not provide a criterion to classify a criminal based on their behaviour.
- Hybrid instances were found in many crime sites in the first decade of forensic research.
- IP work has focused on refining classification model behaviours to better identify one type from another, making classification models more robust, and reducing the number of hybrid cases or redefining hybrids as a separate type.