OKLAHOMA CITY: AFTER THE BOMB
Clues in a Crater
Material found in the aftermath of the bombing can provide clues on the bomb and its maker. For example, wire insulation can be traced to the manufacturer. Such clues can point investigators toward a particular region of the country as a bomb’s source. Here are some of the techniques used to analyze explosives:
Vapor Trace Analysis: Air is drawn over samples of debris--masonry, insulation, wire, paper--and into a collection column. In minutes, an indicator identifies the presence of explosives such as dynamite.
Microscopic Examination: Particles are removed with dissecting needles, fine- pointed tweezers or a scalpel from soft materials such as wood, plastic, rubber and sometimes metal. A trained eye can identify particles of dynamite an black powder by color, size and shape.
Chromatographic Analysis: Widely used to separate and identify products in bomb residue. A plate spotted with sample solution is immersed vertically in a solvent. The sample’s elements will rise to different levels in the solvent. The plate is dried and sprayed with a chromogenic agent that reacts with compounds giving color indications.
Spectroscopic Analysis: Comparing an unknown substance to an electromagnetic radiation spectrum can “fingerprint” pure compounds. This is a low-sensitivity method of identification and requires a substantial amount of explosives residue to register.
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