A contention claimed for opposing mandated taggants is that most terrorist attacks use homemade explosives ( HME ) which would allegedly not be tagged . Examples given included , for instance , the 1993 World Trade Center bombing , the Oklahoma City and the Omagh bombings . Contamination of the site is also cited as a problem , since different taggants might be present at a crime scene from , for example , explosives used to obtain the building materials
1993 World Trade Center bombing
1993 World Trade Center bombing
Taggant