The agency's explanation of a Category 3 source that hasn't been dispersed by fire or explosion reads: "This source, if not safely managed or securely protected, could cause permanent injury to a person who handled it or who was otherwise in contact with it for some hours. It could possibly — although it would be unlikely — be fatal to be close to this amount of unshielded radioactive material for a period of days to weeks."
Exposure for more than a week could be deadly? What is someone going to sleep with it under their pillow or carry it around in their pocket? I would follow the trail