The way to do it is to send a bunch of suicidal jihaddists to west Africa to get exposed to ebola. They will have about 2-3 weeks to travel to other places, such as airports, sports events, etc., where large crowds of people gather. Can you imagine the financial impact? No 3D printers, no bullets needed. Just a few airline tickets and maybe some phony passports.
hope they are not reading your comment
Drinking and driving, even one beer
Drinking and Driving is bad my dear friend