Previous criminological research has focused on the causes of violence at specific points in time across urban areas. However, without the appropriate space-time methodologies, this research literature has been unable to determine how changes in levels of homicide over time may be clustered in space. The current study combined two unique methodologies, ESDA and TRAJ, to explore both temporal and spatial variation in violence across the city of Chicago. Data for the trajectory analysis were drawn from the public-use Chicago Homicide Data Set for the period 1980 through 1995, which contains detailed information on homicides occurring in Chicago, including information about weapon type. Data included information on 12,541 homicides, of which 6,291 involved a street gun and 6,250 involved some other weapon. Temporal changes in homicide rate were calculated per 1,000 population for the study period using 1980, 1991, and 2000 census track population figures. Results indicated that the increase in the total homicide rate across Chicago in the early 1990’s was mainly due to an increase in lethal street gun violence, while homicide by other means was declining. Thus, facilitators in the form of street guns were a major influence in the increase in lethal violence in areas where homicide trends were otherwise declining. Future research should use similar methodologies to focus on the way in which neighborhood characteristics impact the criminal trajectory of communities. Tables, figures, references, appendix