This thesis aims to deconstruct the problem of sexual killing both by examining the validity of conceptualising sexual offending on a continuum and exploring the categorisation of a killing as sexual with analysing the functional significance of the act of killing. It presents a systematic review of literature considering what is known about the characteristics of sexual killers and sexual aggressors before conducting an empirical research study aiming to account for the sexual aspect within the criminal event of sexual killers. The study uses a large sample of 350 non-serial male sexual killers of females aged 14 years or over, who had been convicted and served a custodial sentence within UK Prison Service. Lastly the thesis discusses the diagnostic difficulties of sexual sadism and examines the psychometric properties of a relatively newly developed instrument regarding the diagnosis of sexual sadism, the Severe Sexual Sadism Scale (SeSaS; Nitschke, Osterheider & Mokros, 2009). Clinical and research implications of the research are also considered