Soil As An Evidence

Question:- Why soil is considered as an Evidence?

Answer:- Every type of soil has unique properties which act as an identification markers that’s why it plays important role in criminal investigation.

Forensic scientists consider soil as any earth material that may lead to the conclusion or can help to reconstruct the crime scene and can be way to reach to the criminal. it can be stick to the tires, shoes, or foot or it can be unknowingly or knowingly stick to the clothes of victim or culprit. Soil forensics is considered as an important wing during investigations.

The basic components of soil are minerals, organic matter, water and air. But what do we need for forensic analysis in Soil, it includes rock, minerals, vegetation, glass, paint, asphalt, etc. Soil samples may also contain fossils or debris from human habitation and/or industrial operations, e.g. paint droplets, cinders, chemicals or fibers, however, these are rare but unique. The presence of these in that place helps to make that place of soil unique from others.

Question:- What quantity of soil sample is required ?

Answer:- In most forensics cases, only about one cup of the top layer of soil needs to be collected.

Question:- How soil samples should be collected?

Answer:- Collection tool materials: Tools for soil collection should be new or disposable items, such as; plastic spoons, swabs, wipes, filters. Nondisposable tools for softer materials (unconsolidated sand) may be made of plastic, but for harder materials, tools made of hardened or stainless steel are recommended.

Question:- How analysis should be performed?

Answer:- Samples are dried before testing, to prevent further decomposition of the material in the soil.

👉 At the crime lab, the forensic soil scientist conducts chemical and physical analysis tests and compares the soil samples from the crime scene location with the soil sample found on the suspect or on his or her belongings.

Microscopic Examination– Microscopic examination (Low Power Microscope) is an initial step in soil comparison. If unique foreign particles are found in soil samples which appeared similar in questioned and control sample then further examination will be needed but, if there is no similarity between these samples then no examination is needed.

Screening Methods– Simple and Rapid screening methods are required for soil analysis. Color Comparison and the determination of Particle Size Distribution can discriminate between questioned and control samples.

Instrumental Analysis-

X-Ray Powder Diffraction (XRD) Methods– XRD methods are arguably the most significant for qualitative, and semi-quantitative and quantitative analysis of solid materials in forensic soil science.

Scanning Electron Microscopes and Transmission Electron Microscopes– Scanning electron microscopes (SEMs) and transmission electron microscopes (TEMs) are frequently used to examine the morphology and chemical composition (via energy dispersive X-ray spectroscopy) of particles magnified by over 1,000,00 times, making these techniques very useful for discrimination.

Elemental Analysis– The following instrumental techniques are frequently used to determine the inorganic constituents in soil samples:

  • XRF ( (X-Ray Fluorescence);
  • Atomic Absorption Spectroscopy (AAS);
  • Neutron Activation Analysis (NAA);
  • Inductively Coupled Plasma (ICP);
  • Spectrometry, such as; Inductively Coupled Plasma-Optical Spectrometry (ICP-OES);
  • Inductively Coupled Plasma-Mass Spectrometry (ICP-MS).
  • Fourier-transform infrared spectroscopy (FTIR) can be used to characterize soil organic constituents, for examples: fats, waxes, proteins, cellulose,hemicellulose, and lignin, etc. in soils.

👉 Another test for soil is Ground-Penetrating Radar Technology (GPR).
Ground-penetrating radar (GPR) is a geophysical method that uses radar pulses to image the subsurface. Forensic soil Scientist use radar energy pulses to look for breaks in the soil’s structure. GPR helps detect anomalies in the soil, where radar energy is sent back to the receiving antennae. But it has the drawback that it is not always accurate, especially with heavy clay soils. In the end, with the use of soil forensics and GPR technology, scientists and investigators can make connections between differences in the soil and collected evidence. By identifying the individual characteristics of soil, investigators can use this knowledge to help solve crimes.

This final stage involves information from microscopic observations to the landscape scale, which may involve:

  • Soil classification and use of soil,
  • Geological,
  • And, vegetation maps; terrain analysis, remote sensing and geophysics, etc.

This combined information is used for geographic sourcing to identify the origin of a sample by placing constraints on the environment from which the sample originated.

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