The most routinely used typology in profiling is categorizing crime scenes, and by extension offender's personalities, as either "organized" or "disorganized". The idea of classifying crime scenes according to organized/disorganized dichotomy is credited to the FBI profiler Roy Hazelwood. A typology of serial sexual homicides advocated by Robert Keppel and Richard Walter categorizes them as either power–assertive, power–reassurance, anger–retaliatory, or anger–excitation. Criminal profiling can also be ex-ante or ex-post. Descriptive profiling of a perpetrator is a type of ex-post profiling, and can be used to prevent a serial killer from striking again. Approaches There are three leadings approaches in the area of offender profiling: the criminal investigative approach, the clinical practitioner approach, and the scientific statistical approach. The criminal investigative approach is what is used by law enforcement and more specifically by the Behavioral Analysis Unit (BAU) within the FBI. The BAU "assists law enforcement agencies by their review and assessment of a criminal act, by interpreting the offender's behavior during the crime and the interactions between the offender and the victim during the commission of the crime and as expressed in the crime scene." The clinical practitioner approach focuses on looking at each case as unique, making the approach very individualistic. One practitioner, Turco, believed that all violent crimes were a result of the mother-child struggle where female victims represent the offender's mother. This is also recognized as the psychodynamic approach. Another practitioner, Copson, outlined some principles for profiling which include being custom made, interactive and reflexive. By following these principles, the profile should include advice that is unique and not from a stereotype, should be easy to understand for all levels of intelligence, and all elements in the profile should influence one another. The Scientific approach relies heavily on the multivariate analysis of behaviors and any other information from the crime scene that could lead to the offender's characteristics or psychological processes. According to this approach, elements of the profile are developed by comparing the results of the analysis to those of previously caught offenders. Wilson, Lincon and Kocsis list three main paradigms of profiling: diagnostic evaluation, crime scene analysis, and investigative psychology. Ainsworth identified four: clinical profiling (synonymous with diagnostic evaluation), typological profiling (synonymous with crime scene analysis), investigative psychology, and geographical profiling. Five steps in profiling include: One- Analyzing the criminal act and comparing it to similar crimes in the past. Two- An in-depth analysis of