This chapter investigates the psychological characteristics and motivations that underlie security-related crimes, including insider threats and cybercrime. In relation to criminal behaviour, the Dark Triad (narcissism, psychopathy, and Machiavellianism) are examined as critical personality constructs. Offender actions are additionally influenced by motivational motivations, including ideology, personal grievances, and financial incentives. Furthermore, the chapter addresses criminal profiling methodologies, which incorporate psychological assessments and behavioural analytics. Ethical concerns, such as potential biases and privacy violations, are critically evaluated. This chapter emphasises the necessity of ethical and evidence-based approaches while also offering insights into crime prevention and security strategies through the examination of offender psychology and profiling techniques.