Since Allen's killer's 1980 conviction in federal court in Baltimore, and its affirmation by the U.S. Court of Appeals in 1981, the ATF halted its program to catch bomb-making criminals through the use of taggants. These tagging devices are no longer mixed into explosives in the United States. To aid law enforcement, the colored striped codes in the plastic flakes are changed after each shift at the explosives plant. During manufacturing, they are given magnetic and fluorescent qualities. This means detectives and investigators can more easily find these tiny specks by shining ultraviolet light on debris left at a bombing site.
Investigators can place a magnet inside a small plastic evidence bag turned inside out.
When the magnetized particles are drawn to the plastic bag, it is turned outside in with the evidence sealed inside. Bringing a microscope to a truck's tailgate allows investigators to read the code right at the bombing site. They compare it to the code book and immediately contact the manufacturer and retail outlet. In 16 years, bills have been introduced in Congress to help trace the source of bombings. Insertion of tagging devices into all manufactured explosives and potassium nitrate is opposed by the Institute of Makers of Explosives, the National Rifle Association and the Fertilizer Institute.