FINGERNAIL SCRAPINGS

Fingernail scrapings are rarely exploited to the fullest advantage, although they may provide significant indications in some investigations. The cause of abrasions and scratches found on many parts of the body is frequently a fingernail. The face, neck arms, thighs, and female genitals are the areas commonly attacked and should be subjected to careful medical examination. The form, extent, and location of abrasions will depend on the circumstances in each case.

Resistance offered by the victim during a sexual assault often results in gouging of skin by the assailant's fingernails. Consequently, important evidence often can be obtained by careful examination of fingernail scrapings.

Minute particles of skin, blood, hair, and cosmetics, which often can be found on a suspect and sometimes identified as having come from the victim's clothing, may also be found under the fingernails.

Fingernail scrapings may also assist in determining persons who use narcotics or marijuana.

PROCEDURES FOR TAKING FINGERNAIL SCRAPINGS

In taking fingernail scrapings from a suspect or victim, never use a knife, file, or any other hard, sharp instrument. These are apt to cause bleeding with resultant contamination of the nail scrapings.

The best instrument to use is the blunt end of a flat wooden toothpick, using a different toothpick for each finger. When the scrapings are taken from one finger, the toothpick and scrapings should be placed on a clean piece of paper, which is then folded up and packaged in a suitable container. Each container should be marked to indicate the finger from which the scrapings were taken, and then sent to a criminal investigation laboratory for scientific analysis.

SOILS, ROCKS, AND MINERALS

Soils, rocks, and other minerals may be found on the suspect, the suspect's shoes, clothing, or vehicle; on tools used in the crime; at the scene of the crime; and on the victim. These materials may provide valuable circumstantial evidence. However, such evidence often is overlooked because investigators are neither aware of its potential value nor of the laboratory services available to exploit it.

Difference in Soils and Rocks

Soils and rocks vary in different locations throughout the world. Differences may be found within small local areas. The differences between two types of soil, such as sand and clay, may be readily recognized. Detailed differences and similarities between samples of similar soils or rocks, however, can be detected only by qualified laboratory chemists.

The following factors account for the differences in similar types of soils and rocks that make them useful as evidence.

Over long periods of time, natural forces have produced variations in the composition of soil and rock deposits, both on and below the surface of the Earth

Humans have caused numerous soil and rock variations.

In mining, agricultural, and industrial areas there is an almost constant mixing and moving of soils and rocks. Materials and minerals are added to and taken from the soil. Crops may add identifiable particles to soils in which they grow. Soils and rocks are added to or are taken from surfaces to make them level, thereby disturbing local geological patterns and further adding to the great variety of soil and rock differences.

Local variation may be caused by addition to the soil of plant wastes, plant products, fertilizers, human and animal wastes, soil conditioning materials, and many other substances.

Soils and Rocks as Evidence

One of the primary uses of soils and rocks as evidence occurs in the comparison of samples from the crime scene with samples on the suspect's clothing or other possessions to determine whether the suspect could have been at the crime scene.

Soil and rock evidence is more apt to be found when the offense was committed out-of-doors or when the perpetrator walked or drove a vehicle on unpaved ground

Such evidence may be derived in the following ways: 

l The offender may leave at the crime scene small amounts of rocks and soils that were carried there. In addition to linking the offender with the crime, these soil and rock particles may provide clues to the offender's former whereabouts and occupation. They may indicate whether the offender walked or rode to the scene. 

. The offender may pickup soil and rock materials at the scene. 

. The offender may pickup or leave soil and rock evidence. 

l In a hit-and-run accident, the offending driver or vehicle may pick up and leave incriminating evidence. 

l The impact of the collision may dislodge mud, dirt, and accumulated debris from the undercarriage of the hit-and-run vehicle. Particles may be found on the road or on the body or clothing of a pedestrian struck by the hit-and-run vehicle. 

l The vehicle may run off the road or along the shoulder of the road and, in so doing, pick up mud and dirt on its tires and undercarriage. 

l The offending driver may dismount to survey the damages, to disengage the vehicle, or to make minor adjustments to the vehicle so that he or she can flee the scene. In so doing, mud or debris may transfer to the offender's shoes, clothing, or into the vehicle.

Other Mineral Evidence

Particles of other mineral substances may be encountered. The most common of these areas follows:

Plaster and building materials. Where a building has been broken into, a variety of building materials may be passed through or damaged. Materials may include plaster, plasterboard, insulation, sheeting, cinder block mortar, and brick. Variations in composition, texture, and color combined with the definite probabilities of transfer to the person or clothing of the perpetrator make the collection and examination of these mineral materials essential.

Insulation. The penetration of the walls of a safe may cause the insulation to be broken. Dust from the insulation may be scattered about the scene and it may get on the clothing of the perpetrator. Close examination of the scene may also reveal clearly defined footprints in the dust that has settled on the floor. Substances used for insulating or fireproofing safes vary according to manufacturing specifications. The exact composition is a trade secret; however, a criminal investigation laboratory has data on the types used by major manufacturers and can conduct comparison and study of evidentiary specimens.

Dust. Dust from a house or other building may get on the shoes or clothing of a person who burglarizes or otherwise illegally enters such premises. Such dust may contain ingredients in proportions and combinations that will enable laboratory chemists to determine that the dust could have come from a certain place. For example:

House dust may contain lint from clothing, bedding, drapes, and upholstery; wood fibers from the floor and furniture; paint and plaster particles; human and animal hairs and skin cells; soot; plant wastes; and residue of floor waxes and cleaning compounds. 

. Dust or grime from a vehicle repair shop is apt to contain metal particles and dust; dust from road surfaces; rubber and paint particles; lint and fibers from automobile upholstery and seat covers; and traces of lubricants, fuels, battery acids, and antifreeze compounds.

Collection of Evidence

Clothing, shoes, and other personal belongings that on detailed visual examination appear to contain soil, rock particles, grime, dust, mud, or similar substances should be seized as evidence. They should be individually wrapped Clean plastic bags are excellent containers for that purpose.

You should not attempt to remove evidence from shoes and garments, but should submit the clothes in question to the criminal investigation laboratory.

This is suspected of having been used in the crime, or of having been at the crime scene, should be individually wrapped. Each should be placed in a wooden or heavy cardboard carton. The cutting or prying edge of a tool should not come in contact with any hard or abrasive surface. Wrapping must be secure enough to prevent loss or contamination of foreign materials present on the tool.

If a foreign substance is found on an object or structure too large for shipment to the laboratory, you should scrape the substance into a pillbox or similar container. The pillbox should be carefully sealed and marked for identification. Photographs, sketches, and notes should indicate the exact places from which such evidence was removed. Evidence from different areas must be kept separate.

The residue from under a suspect's fingernails may contain traces of substances from the scene or from the body or clothing of the victim. Scrapings should be taken from all of the suspect's fingers. The scrapings should be kept separate in suitable containers such as small pillboxes.

Collecting Comparison Samples

Always obtain samples of rocks and soils from the scene to be used as standards for comparison with similar substances that may be taken from the suspect. In serious cases, even if there is no suspect, always secure comparison samples. Each sample should consist of about 2 tablespoonfuls of soil.

In taking a sample, it is seldom necessary to go deeper than one-half to three-quarters of an inch. However, if a footprint, tire track or other indentation in question penetrates into subsoil that is different from the topsoil, it may be necessary to secure a sample of both the topsoil and the subsoil.

If soil and rock evidence has been found on a suspect's shoes, a comparison sample should be taken from that portion of a footprint at the scene corresponding to the part of the shoe on which the evidence was found. Comparison samples should be taken from a footprint, tire track or other evidentiary indentation only after a plaster cast has been made. A competent witness should be present when comparison samples are removed, packaged, and marked

Comparison samples should be taken beginning at a starting point, which may be a footprint, a tire track or a place where the suspect would probably have gotten soil on his or her clothing, shoes, vehicle, or tools. Samples should then be taken at varying distances from the starting point to ensure that the samples are representative of the area's soil characteristics. A detailed sketch and notes pertaining to the samples taken, coupled with careful handling to preclude mixing of samples, will help to assure subsequent evidentiary usefulness.

At the scene of a hit-and-run accident, you should secure samples of the soil where the hit-and-run vehicle ran off the road. The road surface should be examined carefully for mud flakes that may have dislodged from the hit-and-inn vehicle. If other vehicles are involved samples for comparison purposes should be taken from the undercarriages of all of them.

When you find a vehicle that you suspect of being the hit-and-run vehicle, secure soil and dust samples from its tires, undercarriage, brake pedals, and floor mats and submit them to a laboratory for analysis and comparison with other evidence and samples pertaining to the case.

Comparison samples from road surfaces and shoulders and from vehicles involved in the hit-and-run accident should consist of approximately 2 tablespoonfuls of soil or dust from each place sampled. All of the evidentiary materials gathered from the road should be collected and submitted to the laboratory.

You should include in your sketch of the crime scene and in your notes the points from which soil and rock evidence and comparison samples were taken. The sketch should contain both compass directions and measured distances.