A method and apparatus for reliably detecting bio-warfare agents in the mail stream that may be released from posted items. The agents are detected as the mail pieces are being processed using typical postal automation machines equipped with image scanning capabilities, and two technologies are combined.One is an aerosol trigger that can be based on a variety of different existing approaches which detects particulates of a specific size range and examines the spectral characteristics of the particles when illuminated with an ultra violet (UV) or other light source. Other approaches may include: mass spectrometry, ion mobility, IR spectrometry and the like. The second technology involves scanning and analyzing images of suspect mail, pieces and correlating aerosol trigger events with mail piece image risk factors.The second technology provides for obtaining images which provide information indicative of mail which is more likely to be from suspicious sources and provide increased risk factors.