One of the most important considerations when investigating a serious sexual offence is to find if it can be linked to other offences. If this can be done then there is a considerable dividend in terms additional evidence and new lines of enquiry. The central problem is the construction of a satisfactory typology of these crimes, but little progress has been made. It is the authors' contention that difficulties arise from the inadequacy of the adoption of the classical or 'crisp set' paradigm. Complex events like crimes cannot be described satisfactorily in this way and it is proposed that fuzzy set theory offers a powerful framework within which crime can be portrayed in a sensitive and perceptive manner that can enhance the search for associations between offences.