The motivation underlying lust killing normally arises from a merging of desires for sex and dominance. Although anger is a negative emotion, aggression has properties of an appetitive activity. Heterosexual lust killers generally have a grievance against women. Homosexual lust killers appear to be unhappy about their sexual orientation, often because of taunting. A distinction is drawn between affective and predatory aggression. An act of killing is commonly preceded by taking alcohol or illegal drugs, viewing violent pornography or acute stress, such as a fight with a partner. Brains are a hybrid of regions old in evolution and development and regions that are new. A Go-System, also known as a behavioural activation system, employs dopamine and underlies engagement with incentives. This system is strongly activated by the prospect of reward in individuals high on a psychopathy score. Sex differences in sexual violence are discussed in terms of brain processes.