The undetonated satchel charge was, in fact, found outside a storefront on Fifty-second Street and Seventh Avenue, although by firemen rather than police officers. In response to a request for operational support from the NYPD, technicians wearing bomb protective suits from the FBI’s New York field office were quickly dispatched to collect the evidence. When it was determined that the device’s fusing system was inoperative, and that it was therefore safe for transport, the specialized unit—in a procedure okayed by the local assistant director—arranged for the satchel charge to be delivered to FBI HQ in Washington, D.C., where it was given over to the EU-BDC for scientific examination. A further discovery at the bomb scene by agents equipped with ultraviolet lights had caused the laboratory to buzz with anticipation well in advance of the package’s arrival: fluorescence had been detected in both the unexploded charge and debris samples collected near the site of the initial blast, strongly indicating the explosives had been tagged with chemical markers by their manufacturer. Their reaction was strongly warranted—while not yet legally mandated in the United States, tagging had been required by the Swiss government for years and was a voluntary practice among an increasing number of international explosives suppliers. If indeed present, the expectation was that the markers would lead investigators back to the point of sale, and produce valuable information about the purchaser of the bomb-making material.

Soon after the C-4 satchel charge reached the lab, a microthin sliver was taken from it, placed on a specimen slide, and then exposed to a Tesla coil magnet for the purpose of orienting the tags of melamine plastic—each chemically inert particle about the size of a speck of pollen and striated with color—that it might contain. Typically taggants were mixed with explosive ingredients at concentrations of 250 parts per million, a ratio that allows the explosive to retain its full stability and performance, while showing up for easy viewing under microscopic examination. In this instance, an Olympus binocular light microscope equipped with 35mm Polaroid video was used by a forensics specialist who immediately verified the presence of markers and, working with feverish excitement, read and photographed the taggants for their color-coded information about the manufacturer, production date, and batch number of the plastique.

From there it became a fairly routine computer search. The information was checked against the main charge identification database for commercial explosives which had recently been added to the Explosives Reference and Search System—dubbed EXPRESS by government techies with a fondness for acronyms—and drew a hit on the first shot.