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testes which can identify the type and origin of the sample. The first and probably the most common is the density gradient tube. Two different liquids are added to a glass tube in various ratios. Each ratio represents a different density. The soil sample is poured into the tube. When the various particles reach a level in the liquid where their density is equal to the liquid the particles become suspended. This creates a unique profile of bands in the tube which can be matched to other samples.

The samples may also be tested using heat to test the point at which the sample will undergo an exothermic reaction or an endothermic reaction. The sample is heated in a special furnace to various temperatures. In an exothermic reaction the sample essentially burns and releases heat. In an endothermic reaction the sample will absorb the heat. Each sample from different locations will have these reactions at different temperatures according to the mineral, biological and synthetic content.

Electron microscopes can be used to reveal the crystalline structures of minerals and synthetic material in a sample of soil.

Nuclear Resonencing and Mass Spectometry are also methods which may be used in the Laboratory.

It is important that the crime investigators and the laboratory analyst communicate properly. Perhaps this happens best when the laboratory head is knowledgeable about investigations and is the contact person for investigators. The head can be briefed on the questions and issues of the case and then direct the laboratory personnel as to the direction of the inquiry. The investigators may want to know if sample #12 and sample #76 are similar. The laboratory head will then choose appropriate methods which express the similarity between samples. Once the questions and procedures are chosen everything depends on the integrity of the sample. If they have been collected with care and documented amply then the results from the laboratory can be trusted (Steck, 2004).

Conclusion

Take samples of all the soil in and around a crime scene. Place a reference sample in a plastic vial and label it with the date the time the investigators name and the case number. Reference samples are samples of soil from places the suspect or victim may have picked up soil. The reference sample can also be from sites the suspect may have been. Include the location and the distance from the focal point of the crime when labeling samples. .

Reference samples should be about a tablespoon or so taken from less than a 1/2 an inch (about 1 cm). The exception is in cases of burial where samples should be taken every 1 inch (every 3cm). With gravesites the bottom of the grave should be sampled after the removal of the remains. Package and label all samples carefully. Keep in mind that the analysts in the laboratory do not have firsthand knowledge of the scene and the circumstances of collection.
Package movable objects to protect them from loss of soil by jostling.

Package all movable objects such as clothing, footwear and tools intact and protected from jostling.

Learn more about this author, Katherine Steck-Flynn.
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