A method and apparatus for detecting an occurrence of an event of interest. The apparatus comprises a surveillance system, a detector, and an analyzer. The surveillance system monitors subjects within an environment to generate monitoring data. The detector detects a number of indicator instances exhibited by at least a portion of the subjects using the monitoring data. Each of the number of indicator instances is an instance of a corresponding event indicator in a set of pre-selected event indicators. The analyzer evaluates the number of indicator instances and additional information to determine whether at least a portion of the number of indicator instances meets an event detection threshold, thereby indicating a detection of an occurrence of an event of interest.