1. A computer readable storage device containing an executable program for surveilling an environment monitored by a sensor, where the program causes a processor to perform steps comprising: extracting data about an individual present in the environment from an electronic signal provided by the sensor; classifying the individual according to a role fulfilled by the individual within the environment without recognizing an identity of the individual, using the data extracted from the electronic signal; generating a trajectory that illustrates movements and locations of the individual within the environment; and detecting, subsequent to the classifying, when the trajectory indicates an event that is inconsistent with an expected pattern of behavior for the role.