Forensic Soil Analysis

Case #761 Soil Examination

• In a murder case, the suspect is in custody and refusing to speak
• A search warrant of the suspect's property found an empty house and a car covered in dirt

Analysis of Dirt From Car

• Composed of 60% sand, 30% silt, and 10% clay
• Analysis included microscope imagery of the sand
• High levels of Calcium Carbonate

What is Soil?

• The top layer of Earth's crust
• It contains living (biotic) and nonliving (abiotic) components

Abiotic Components

• Water & Air
• Minerals
• Includes disintegration from erosion and weathering

Biotic Components

• Bacteria
• Decay
• Includes nitrifying bacteria

Soil Texture

• There are 12 classifications based on the percentage of 3 different particles

Soil Particle Size and Characteristics

• Sand is coarse and water moves easily through it.
• Sand is typically found in deserts and beaches.
• Silt is medium and retains some water.
• Silt is commonly found in riverbeds.
• Clay is fine and retains water.
• It is found in various locations.

Soil Triangle and Texture

• Soil with 30% sand, 60% silt, and 10% clay is classified as silty loam
• Fertile soil, called "loam", contains mostly sand and silt with low clay content
• Soil that consists of 10% sand, 60% silt and 30% clay is silty clay loam

Soil Profiles

• Soil layers are arranged in horizons (O, A, E, B, C, R)

Horizons

• The O horizon is humus consisting of decaying organic matter.
• The A horizon is topsoil consisting of humus, minerals and plant roots.
• The E horizon consists of sand and silt, and water removes minerals from it.
• The B horizon is subsoil containing clay and mineral deposits.
• The C horizon is broken rock with no plants and little humus.
• The R horizon is solid rock with no plants and little humus.

Importance of Textures and Profiles

• Textures provide insight into locations
• Loams are found in gardens/woods
• Clay/silt come from non-surface layers
• Sands are unique
• Profiles reveal location and depth

Sand as a Soil Fingerprint

• Sand forms through the weathering of rocks/minerals, skeletal remains, and broken shells
• Sands can form in unique sizes from different sources
• Identifying sand is key to determining potential locations from the soil

Sand Maturity

• Immature sand has fragments, lots of clay, and found near rock
• Mature sand is smooth, with very little clay that located at beaches and dunes

Sand Types

• Continental sand is found at beaches and is made of quartz, mica and feldspar
• Volcanic sand is found near volcanoes and contains black basalt, green olivine and very little quartz
• Skeletal (biogenic) sand is made from remains of living organisms such as microorganisms, shells (CaCO3) and coral
• Precipitate sand is minerals deposited from evaporated water made of calcium carbonate that form oolites

Soil Chemistry

• Soil's ability to grow plants depends on the balance of essential nutrients and pH
• Calcium helps stems and leaves from drooping
• Nutrient deficiencies are impacted by pH levels

Effects of Bodies on Soil

• Bodies release toxic chemicals that kill plant life & nutrient rich fluids that change the soil
• Creates a cadaver decomposition island (CDI)
• In a CDI, there is an area of no growth and changing pH

Effects of Soil on Gravesites

• Digging mixes subsoil and topsoil, causing different colors
• Moist soils contribute to adipocere (grave wax) formation
• Wet/dry cycles can cause bones to expand and contract
• Acidic or alkaline soils slow down decomposition
• Low oxygen levels cause body to release gases that dogs can smell

Collecting Soil Evidence

• Photograph and document the crime scene
• Sketch the crime scene
• Collect at least 4 tablespoons of material from different locations
• Collect surface soil
• Any soil that looks different than the surrounding soil
• Collect soil from different levels
• Collect soil from objects at the crime scene

Analyzing Soil Evidence

• Microscope analysis can reveal locations based on shells, coral and plants
• Soil can reveal physical evidence such as bullets, sawdust, oils, glass, jewelry, keys and knives
• Soil can reveal biological evidence such as bones and teeth

Analyzing Soil Physical Properties

• Physical analysis of soil can be done by sorting and measuring size, location, and angle
• Determine % of sand, silt and clay contents
• Creating a soil profile
• Using a magnet to detect metals
• UV light analysis