The following is adapted from Forest Products Laboratory 1910 – 2010 : Celebrating a Century of Accomplishments.
As we saw in the case of the Crimson Criminal, researchers from the Forest Products Laboratory (FPL) have the ability to trace even the tiniest fibers of crime-scene wood to their source to help bring criminals to justice. In some instances however, when evil-doers leave only dust in their wake, conventional analysis is not an option, and an exact identification of the material can be impossible. Researchers instead must instead rely on experience, deduction, and inference to reach a logical conclusion.
The wood filler (sawdust) used in bombs confiscated in Central America was examined to see if the bombs were made outside the region and trace the explosives to their producer. The theory was that wherever the bombs were made, local sawdust would be used.
The fragments were so small that they could not be sectioned. Regis Miller, from the Center for Wood Anatomy Research at FPL, examined the fragments under a light microscope, looking for anything that could be recognized as a species of north temperate origin. He was unable to identify the species of any fragments, but concluded that the wood filler was probably tropical in origin.
Miller was able to make that statement because the fragments did not have spiral thickenings, a feature common to many north temperate species. In addition, almost all the fragments were hardwoods. This is expected of tropical sawdust because most trees in the tropics are hardwoods; in the north temperate regions, softwoods are much more common.
The only softwood fragment in the dust closely resembled a species of Podocarpus, one of the few softwoods confined to the tropical regions. He also found a fragment from a monocot (perhaps a palm), several fragments that contained a large amount of prismatic crystals in axial parenchyma cells, and fragments with small parenchyma cells or chambered cells.These features are fairly common in tropical species, but are rare in north temperate species.
Even though the exact species of wood remained a mystery, Miller concluded that the sawdust used in the explosive devices was consistent with material of Central American origin, and was confident enough to submit this opinion to law enforcement officials to help apprehend the explosives manufacturer. Miller’s observation and analytical skills are a testament to the power of science professionals, who fill the gaps when conventional analysis fails, and prove that the backbone of all science is the not the research, but the researcher themselves.