Fingerprints are the most common form of physical evidence, and recovering them is a foremost duty of investigators at a crime scene. The investigator uses a fingerprint powder, also termed fingerprint dust, to extract fingerprints from a variety of surfaces. Crime scene investigators have the option to use either a regular or magnetic powder. Fingerprints that are lifted at crime scenes are termed “latent” prints. The most common method to lift prints is a mechanical one, using powder and cellophane tape.
Choosing a Powder -- Regular
Investigators typically apply regular powders to table tops, kitchen counter tops, televisions, windows and other painted surfaces. This powder works best on the exterior of motor vehicles. Fingerprint powders are available in various colors, including biochromatic, black, white and silver/grey. Crime scene investigators will choose a color based on the background surface from which they need to lift the fingerprint. Black powder is most frequently used though, as this print contrasts well against the white backing cards. The investigator will choose a silver colored powder to lift prints from dark backgrounds. Biochromatic powder has been designed for use on both light and dark surfaces.
Choosing a Powder -- Magnetic
The investigator will often opt for a magnetic powder, which contains iron, to apply to plastic containers and similar shiny surfaces. These powders are available not only in the same colors as the regular powder, but in fluorescent colors, such as green and red, as well. Investigators use fluorescent colors on surfaces that have background fluorescence.
Applying the Powder
Crime scene investigators normally carry jars of both regular and magnetic powders, together with both black and white backing cards. Regular powder is applied using a fiberglass brush, while the magnetic powders are applied with the use of a magnetic applicator. The investigator uses a feather duster to apply the fluorescence powders. It is best to sprinkle fingerprint powders onto a tray and not use it directly from the jar. The powders, particularly the magnetic products, need to be applied with a light hand and gentle strokes. Investigators who work with these powders should wear a mask to prevent inhaling any of the powder.
Lifting Prints and Logging Details
The process by which the fingerprints are recovered at a crime scene is termed the lifting process. Both the regular and magnetic powders can be used to secure prints for the purpose of matching fingerprints. The powder creates prints that are subsequently lifted with the use of either frosted or clear cellophane adhesive tape. The investigator places a strip of tape onto the powdered surface and rubs it to the powder. She will then lift the tape and apply it to the backing card with some pressure. Specific data, such as the date, time and location, must be logged and must accompany the fingerprints.
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