by the creation or elimination of boundaries and circulation networks, and by facilitating surveillance by the citizenry and the police." He asserted that crime was inversely related to the level of activity on the street, and that the commercial strip environment was particularly vulnerable to crime because it thinned out activity, making it easier for individuals to commit street crime. Angel developed and published CPTED concepts in 1970 in work supported and widely distributed by the United States Department of Justice (Luedtke, 1970). 1970s The phrase crime prevention through environmental design (CPTED) was first used by C. Ray Jeffery, a criminologist from Florida State University. The phrase began to gain acceptance after the publication of his 1971 book of the same name. Jeffery's work was based on the precepts of experimental psychology represented in modern learning theory. (Jeffery and Zahm, 1993:329) Jeffery's CPTED concept arose out of his experiences with a rehabilitative project in Washington, D.C. that attempted to control the school environment of juveniles in the area. Rooted deeply in the psychological learning theory of B.F. Skinner, Jeffery's CPTED approach emphasized the role of the physical environment in the development of pleasurable and painful experiences for the offender that would have the capacity to alter behavioral outcomes. His original CPTED model was a stimulus-response (S-R) model positing that the organism learned from punishments and reinforcements in the environment. Jeffery "emphasized material rewards . . . and the use of the physical environment to control behavior" (Jeffery and Zahm, 1993:330). The major idea here was that by removing the reinforcements for crime, it would not occur. (Robinson, 1996) An often overlooked contribution of Jeffery in his 1971 book is outlining four critical factors in crime prevention that have stood the test of time. These are the degrees to which one can manipulate the opportunity for a crime to occur, the motivation for the crime to occur, the risk to the offender if the crime occurs, and the history of the offender who might consider committing the crime. The first three of these are within the control of the potential victim while the last is not. For reasons that have received little attention, Jeffery's work was ignored throughout the 1970s. Jeffery's own explanation is that, at a time when the world wanted prescriptive design solutions, his work presented a comprehensive theory and used it to identify a wide range of crime