Criminal history narrative studies reveal an escalation in sexual offender behaviour from non-contact to contact offending, with an ever-increasing likelihood of sexual violence and homicide. In particular, researchers have found that sexual offenders often have a history of committing burglaries prior to contact offences. Accordingly, researchers have suggested that burglaries may be associated with an increased likelihood of future sexual offending, particularly when they have a sexual element to them. However, to date, there has been little quantitative research focusing on the mechanisms of escalation in sexual offences. This paper seeks to study factors associated with sexual offence escalation in terms of changes in offence seriousness and frequency. Specifically, case evidence was gleaned from a series of fetish burglaries and subsequent sexual assaults and murders committed by the former Canadian Colonel David Russell Williams (RW). Cluster analysis, chi-square, ANOVA, and regression analyses were conducted on the crime scene information of RW's 82 cases of fetish burglary. Analyses revealed a significant escalation in the frequency and seriousness of RW's fetish burglary offences prior to committing acts of sexual violence and ultimately sexual homicide. Recommendations for future research predicting escalation of sexual offending by frequency and seriousness of offending behaviour are discussed. Copyright © 2013 John Wiley & Sons, Ltd.