1. An apparatus comprising: a surveillance system that monitors subjects within an environment to generate monitoring data; a detector that analyzes the monitoring data to identify a number of indicator instances exhibited by at least a portion of the subjects, wherein each of the number of indicator instances is an instance of a corresponding event indicator in a set of pre-selected event indicators; and an analyzer that evaluates the number of indicator instances identified 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.