Differential Sampling of Footwear to Separate Relevant Evidentiary Particles from Background Noise

As submitted by the proposer:
Although it is well-recognized that criminals track dusts to and from every crime scene, dust particles on a suspect's shoes are very seldom used as evidence linking the accused to the crime. The major obstacle preventing the use of this type of evidence is that the shoes have mixtures of particles arising from activity before, during and after the crime itself. Methods separating the evidentiary particle "signal" from background noise would enable a powerful new and widely applicable forensic capability. This capability would augment traditional footwear pattern evidence with objective quantitative associations, addressing one of the specific issues raised in the 2009 NAS report. Our prior NIJ research has shown corresponding particle sets to provide extremely strong, objective, quantitative, associative evidence. We hypothesize that by separately analyzing loosely held, moderately held, and strongly held particle fractions, we will be able to detect sequential footwear exposures and enable the widespread use of this new forensic capability. Our research goal is to test the separation of particle signals on footwear by applying a series of successively more aggressive sampling steps and contrasting the resulting types and quantities of particles. There are three specific objectives:
1. Conducting suitable environmental exposures. Three sites will be chosen that have different, characteristic particle types (soil minerals). Footwear of two types will be tested, accumulating particles by walking 250 m in each environment. Some shoes will be exposed to one environment; others will be exposed to all three, in one of six different sequences.
2. Develop differential sampling methods. A protocol will be developed that separates particles based on how tightly they are held to the sole. Parameters will be adjusted for four progressively more aggressive sampling methods (walking on paper, electrostatic lifts, gelatin lifters, and swabbing). The resulting numbers and types of particles will be determined using forensic microscopy.
3. Test the ability to separate small particle signals of interest. The methods developed in Objective 2 will be applied to shoes from Objective 1. Particles from the different fractions will be statistically analyzed and the ability to objectively distinguish the order of exposure to the three environments will be determined.
This research will provide a greater understanding of how particles adhere to the soles of footwear, how they can be separated, and whether sequential exposures can be determined on this basis. If successful, a new forensic capability will be enabled that is widely applicable, with objective, quantifiable associations.
ca/ncf