Text of a speech describing perpetrators of potential criminal acts against nuclear programs in terms of their possible motivations, actions, methods, resources, and capabilities. Though assessment of crime in the nuclear domain is necessarily speculative, it is possible to say that a broad range of threats and adversaries must be anticipated. Ideologically motivated criminals would include political terrorists, anti-nuclear extremists, and other fanatics. Economically motivated types would include those attempting theft for ransom, sale (no known nuclear black market exists, but one is possible), or extortion. Personally motivated individuals might act out of specific grievances or mental instability. Possible criminal actions range from hoax bomb threats to theft of nuclear material for use in some sort of nuclear dispersal or explosive device. Physical resources (men and weapons) pose less of a problem for adversaries than special human resources (technical skills, willingness to accept great risk, inside information). If it follows the pattern of sophisticated nonnuclear theft, nuclear theft is likely to involve the collusion of insiders, from security guards to management.