Janet R. Oliva 
Sexually Motivated Crimes [PDF ebook] 
Understanding the Profile of the Sex Offender and Applying Theory to Practice

In cases where minimal or no physical evidence exists, behavioral evidence may be all that investigators have available to help them focus the investigation. It may be the only aspect of the case that can link one unsolved case to another, or to numerous other unsolved cases. Sexually Motivated Crimes: Understanding the Profile of the Sex Offender