Fingerprint Development Techniques (see Appendix A)

When choosing a technique to use in the development of latent fingerprints, the technician must recognize the surface on which the fingerprints may have been deposited. Surfaces are categorized as porous (air can pass through such as papers, untreated wood, skin) and nonporous (air cannot pass through it such as plastics, glass, mirror, metals). Textured surfaces, such as leather, also need to be considered. Recognizing the surface type is important when choosing the most effective processing technique in which to yield fingerprints. One must utilize sequential processing. This means that the least intrusive method is applied first through to the most intrusive. As an example, the least intrusive method is visual examination, using inherent lighting followed by illumination with oblique lighting. The most intrusive would be a dye stain or other chemical technique. Those prints seen without treatment (plastic and patent) should be photographed and, where appropriate, removed from the scene. When photographing, take a photograph with and without a scale of the prints and object. The preferred scale is an ABFO, L scale. To assist in the detection of semi-hidden prints, oblique, infrared, or ultraviolet lighting may be utilized. Prints on nonabsorbent, hard surfaces will remain entirely on the surface in the form of a delicate liquid or semisolid deposit consisting mainly of water and oil, extending upward from the surface, which makes an ideal adhesive base for fingerprint powders. Whenever there is a potential of losing the latent print during the lifting or retrieval process, that latent should be photographed.

The following development techniques are not all-encompassing but rather an example of the more common techniques used in the development process. To learn and understand all of the possible methods for development, one must invest many hours in training and practice to perfect the techniques.

Powder Techniques

I. Brush and Fingerprint Powder Development (Figure 5.11). This is the most common method of developing latent prints currently in use.

A. Materials: Fingerprint powder, fiberglass brush, different types of animal hairbrushes, lifting tape, latent cards (black or white and in various sizes), and writing implement.

• 1. Apply a small amount to the brush, twirl excess powder off the brush in the powder container. The important thing to remember is that too much powder applied to the latent fingerprint can make identification difficult as the ridges may be filled in due to excessive powder. Gray prints are better than dark black ones.
• 2. When applying the brush to the area to be processed, twirl your brush over the area gently touching the surface with the tips of the bristles from the brush. Twirling allows an even distribution of the powder. Gentle application is important here to ensure that we are not brushing away the latent fingerprint. For large areas such as vehicles, applying a layer

Figure 5.12 Processing with black powder on a nonporous object.

of powder to clean sterile cotton and lightly applying (wiping) the powder to the area is also an acceptable method. Applying the powders to latent (invisible) fingerprints is allowing for them to now be visible so that lifting can be possible.

Be sure the area is dry prior to utilizing the powder technique. If the area is not dry allow the item to dry prior to processing with powder or collect the item (property receipt issued to the owner of the property) and process at the lab.

Figure 5.13 Processing with black powder.

Figure 5.14 Processing with black powder.

Figure 5.15 Tearing latent tape to leave the triangle on the roll. This prevents technicians from putting their own fingerprints on the sticky side of the tape. Step 1 for tearing latent tape.

Small Particle Reagent (SPR) is another technique (described later) that can be used on wet surfaces.

3. The visible print is then lifted using sterile latent fingerprint tape. To prevent the technician from inadvertently

Figure 5.16 Second step in tearing tape to leave a triangle on the tape.

depositing their own fingerprints on the sticky side of the tape, technicians know how to incorporate a triangle at the end of the tape (next to the roll) when tearing the tape off the roll. Once torn from the roll, a triangle remains on the piece of tape which allows the technician to hold the tape without touching the sticky side of the tape (see photographs on how to tear the tape with a triangle later).

With advances in DNA technology, touch DNA can be yielded from fingerprints. The crime scene technician should always carry disposable powders and brushes (one-time use). This prevents contamination from other scenes and allows for any lifted fingerprints to be further evaluated for DNA.

4. Lay the latent tape over the processed (now visible) fingerprint (Figure 5.19), lay this on the unprinted glossy

Figure 5.17 Third step in making a triangle on the roll of tape.

side of the card (Figure 5.21). Place the processing technician’s initials on an area where no fingerprint characteristics are, between the tape and card ensuring that the tape containing the lifted fingerprint has not been alerted or tampered with (Figure 5.22). Label the other side with case information (case number, type of case, date, location, technician, victim name, and any other pertinent information as per your agency protocols).

II. Magnetic Powder Development. This technique is generally not good for prints on metal surfaces or magnetic tapes as the magnet may erase information. This technique works well on porous surfaces.

A. Materials: Magnetic wand, magnetic particles mixed with powder, lifting tape, latent lift cards, and writing implement.

Figure 5.18 Fourth step in tearing the tape from the roll leaving new triangle on the roll of tape.

Figure 5.19 Tape with triangle laid over processed fingerprints.

Figure 5.20 Processed fingerprints with black powder on tape.

B. Method: This method is used in a similar fashion as brush and powder. However, the magnetic wand should not touch the surface. The magnetic powder is the only part that should be applied to the surface. The magnetic wand may cause scratches on a surface and degrade or contaminate latent prints. When utilizing the wand, we paint the powder (like a paint brush) onto the surface. The powder only touches, not the wand.

Figure 5.21 Processed fingerprints on tape placed on latent card.

Figure 5.22 Processed fingerprints on the latent card.

Note: There are a variety of powders that may be utilized to develop prints on various surfaces. The most common powders are black, white, and bi- chromatic. Some powders may also be used in conjunction with other

Figure 5.23 Technician's initials across tape and card to ensure the integrity of fingerprint lifts.

Figure 5.24 Magnetic powder used on porous surfaces (paper, cardboard).

Figure 5.25 Processing with magnetic powder.

Figure 5.26 Processing with magnetic powder on cardboard.

Figure 5.27 Latent tape being laid on developed fingerprint.

chemical techniques such as cyanoacrylate ester (CAE, or Super Glue). The reason for the variety of powders is to provide the greatest contrast with the background on which the fingerprint is developed.