To determine the implications of variation in mortality associated with use of weapons in different contexts. Literature review. Armed conflicts and civilian mass shootings, 1929-96. Mortality from wounds. During the fighting of war the number of people wounded is at least twice the number killed and may be 13 times as high; this ratio of the number wounded to the number killed results from the impact of a weapon system on human beings in the particular context of war. When firearms are used against people who are immobilised, in a confined space, or unable to defend themselves the wounded to killed ratio has been lower than 1 or even 0. Mortality from firearms depends not only on the technology of the weapon or its ammunition but also on the context in which it is used. The increased mortality resulting from the use of firearms in situations other than war requires a complex interaction of factors explicable in terms of wound ballistics and the psychology of the user. Understanding these factors has implications for recognition of war crimes. In addition, the lethality of conventional weapons may be increased if combatants are disabled by the new non-lethal weapons beforehand; this possibility requires careful legal examination within the framework of the Geneva Conventions.