It was more than a hundred years ago that soil evidence was effectively used for criminal investigation. But it was in a fictional literature of Sherlock Holmes series written by Sir Arthur Conan Doyle. At almost the same time Hans Gross of Austria wrote in his Handbook for Criminalistics that dirt on shoes probably can tell useful information for criminal investigation, but it did not include any actual case study in which soil could be physical evidence.
Soil can provide useful information about link of persons to crime scenes because of its nature as the surface of the ground. The evidential value of soil stands on large variation in its characteristics. Soil has extreme complexity not only in components such as minerals, oxides, organic matter, microorganisms and their materials but also physical nature such as particle sizes and densities. Considering the granite rock alone, for instance, there is an almost unlimited number of kind. They are easily recognized according to difference of color, mineralogy, texture and a lot of other characteristics.
The character and composition of soils vary laterally and with depth. Although the color and texture of soils may not appear to vary along the ground, the chemical composition can change sufficiently in a short distance. Therefore, several samples should be submitted to establish the normal distribution of soil of a particular type in and around a crime scene. Depending upon the case circumstances, other evidence may be present. An investigator may need to consider latent prints, tool-marks, broken glass, shoe/tire prints, blood stains, saliva, and other trace evidence.
Training program of forensic soil examination is needed for examiners who are in charge of soil evidence and crime scene investigators. Alertness of those who collect samples, and quality and collection is critical to success of forensic soil examination. Macroscopic observation and low-power stereomicroscopic observation is important at the initial step of forensic soil examination. It will be lucky for examiners if unique particles such as paint chips, fibers with distinctive color, glass fragments can be found both in a questioned soil sample and a control one. The examination can be focused on these unusual matter in soil, and at this step soil is only background of evidence.