Screening of soil evidence by a combination of simple techniques: validity of particle size distribution.

The validity of the determination of particle size distribution for forensic soil identification was studied using 73 soil samples collected from a 20 km x 15 km area. Soil particles were first divided into two fractions by wet sieving with a sieve with a 0.05 mm aperture size. Dry sieving was used to analyze the coarse particle fraction and a particle size analyzer was used for the fine particle fraction. The number of particle size classes measured by sieving could be reduced to three, <0.05, 0.05-0.2, and 0.2-2 mm, which enabled 87.9% of the soil samples to be discriminated. Measurements made with the particle size analyzer on the fine particle fraction increased the discriminating power to 95.9%. The use of particle size analysis by sieving in combination with color examination allowed us to discriminate 99.5% of the soil samples, even when particle size analysis of the fine particle fraction was not carried out.