Fundamentals of Criminal Investigations
Adam J. McKee, Ph.D.
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Section 6.3: Fingerprint Evidence
The skin is both the largest organ and the first line of protection in the human body. Completely covering the body from head to toe, the skin is primarily consistent in nature everywhere except for the areas covering the palmar surfaces of the fingers and hands and the plantar surfaces of the toes and feet. The skin on these areas is referred to as friction ridge skin. Obtaining legible recordings of these areas of skin is crucial for subsequent comparisons to latent impressions recovered from crime scenes, for comparison against previous records, or for input into automated fingerprint identification systems (AFIS). Inked prints, record prints, standards, and exemplars are all terms that are used to describe the recording of these unique details.
Various types of equipment, inks, scanning devices, and techniques are used to record friction ridge detail. Although the concept of recording friction ridge detail seems basic, care and determination should always be exercised in order to obtain the best quality recordings because complete and legible recordings are a necessity in latent print examinations.
Processing Latent Fingerprints
Prints on evidence are fragile. The slightest amount of handling can degrade a print.
Whenever possible, collect the object on which you find prints. Photograph the powdered print before collecting it. Always use clean gloves when handling evidence. Remember: Your prints and DNA may be transmitted by gloves when you touch anything, such as when you scratch your nose. Identify the object that needs to be dusted.
Smooth surfaces yield the best latent prints. When looking for latent prints, examine windows, mirrors, glasses, door handles, doors, etc. Position the print powder, brush, and lifting tape within reach of the object.
Use a powder color that contrasts with the background of the item from which the print is being collected. The color of the backing material must contrast with the color of the print powder used. Gently brush the powder onto the object. When available, follow manufacturer’s development process instructions.
Pour a small amount of powder on a clean piece of paper or jar lid. Lightly dip the brush into the powder. Tap the brush lightly to cause excess powder to fall off of the brush onto the paper. Carefully and gently brush the object being printed using curved strokes that follow the natural lines of the print.
Note: Don’t ever blow on the surface since it can contaminate the surface with DNA.
Be sure to photograph the developed print. Also, be sure that each photograph shows the scale and identification label. Always shoot location photographs as well as one-to-one/close-up photographs.
Label a lift card for the print with your initials and identification number, the date and time, evidence number, and evidence description. Record the information on the back of the card holding the lifted print. Each piece of evidence must have a unique number. This number should correspond to the placard next to the evidence. The evidence description includes:
- Type of print being collected
- Location of the print
- Orientation of the print to north or to a prominent nearby object; e.g., “Fingerprints found on telephone receiver.”
- A brief diagram of the location of the print on an object, depicted with an “X.”
Lifting a Developed Print
Remove a piece of lifting tape. If a premade tape lift is being used, open the tape lift and remove the protective seal over the sticky part of the tape. If contact paper is being used, remove the protective backing that covers the adhesive side of the paper. Press the sticky side of the lifting tape to the developed print. Use firm but gentle pressure taking care not to smear the print. Place the sticky side of the lifting tape onto the card stock.
Packaging Lifted Prints
Protect the print by pressing the lifting tape to the card stock while taking care not to smear the print. Packaging Place the print lift in a container. Multiple print lifts can be placed in the same container. Submit all print lifts to the laboratory. Do not attempt to determine which lifts are suitable for comparison purposes. Close the container and seal the entire opening with evidence tape. Write your initials and identification number, and the date and time across the evidence tape seal. If printing a surface that may contaminate the fingerprint brush or powder with physiological fluids or controlled substances, do not use them on subsequent items until they have been decontaminated.
If possible, collect the item on which the print was found. If the print is still moist, allow it to dry before collecting it. When packaging an item with a developed print on it, be sure the transport container is made of paper and large enough to hold the item without damaging the print. Place the item with the print, print side up, into the container while protecting the print from being touched. Secure the item so that the print will not move or be disturbed during transport. Seal the container with the evidence tape. Label the evidence tape.
Processing Patent Fingerprints
Patent is another word for visible.
Prints on evidence are fragile. The smallest amount of handling can degrade a print. Always photograph the print before collecting it. Always use clean gloves when handling evidence. Your prints may be transmitted through your gloves when you touch anything, such as when you scratch your nose. Documentation Photograph the visible print.
When photographing the print, ensure that each photograph shows the scale and identification label. Always shoot location photographs as well as one-to-one/close-up photographs. Collection If possible, collect the item containing the visible print. If the print is still moist, allow it to dry before collecting it. Packaging Select a suitable container to transport the print. Make sure it is made of paper and is large enough to hold the item without damaging the print. Place the item with the print on it, print side up, into the transport container while protecting the print from being touched. Secure the item so that the print will not move or be disturbed during transport. Seal the container with the evidence. Label the evidence tape.
Chemical Processing of Prints
Chemical processing is best performed in a laboratory or controlled environment. Chemical processing involves safety considerations since the chemicals used may constitute a hazard. Chemical processing should only be performed by someone trained in the use of the process in the field.
Ninhydrin: Used on porous surfaces such as wood, wallboard, and paper.
Caution: If ninhydrin is used at the crime scene, proper safety precautions must be taken. Solvents used in the preparation of ninhydrin can be flammable or deplete oxygen.
Cyanoacrylate (Super Glue): Used on non-porous surfaces such as glass, metal, and glossy or coated surfaces.
Small particle reagent: Used on wet surfaces.
Crystal Violet: Used on the sticky side of adhesive tapes.
Sudan Black: Used on plastic baggies, coated drinking cups and plates, food stuff-contaminated non- and semi-porous items, and cyanoacrylate-processed items.
Latent prints can also be enhanced by the use of a forensic light source in combination with the following processing chemicals and powders: DFO Indanedione Rodamine 6G, RAM, Basic Yellow, etc. Redwop, Greenwop.
Inking Prints for Comparison
The equipment that is needed to record friction ridge detail includes an ink roller, an inking plate (constructed of glass or a smooth metal, such as stainless steel), fingerprint or palm print cards for recording the prints, and a quality black ink formulated for this purpose. These items can be obtained from various forensic or printing supply companies. Only inks formulated for forensic purposes should be used, because other types of inks (printer’s ink, writing ink, or rubber stamp ink) are too light, too thin, or do not dry quickly enough on the recording cards; this retained moisture could cause subsequent smearing of the prints. An alternative to the ink-and-roller method is the use of micro-reticulated thermoplastic resin pads or ceramic inking pads, both of which are impregnated with special permanent and nonfading inks.
A fingerprint stand is also useful. The fingerprint stand can be placed at a height that is necessary to comfortably record friction ridge detail while conveniently holding within its built-in storage bins all of the equipment needed for this purpose. The standard cards that are used to record prints are 8” x 8”. This size has space for two rows of five rolled fingerprints and space for plain or flat prints of the fingers under the rows of rolled prints. These cards are white and are usually lightweight cardboard or heavy paper stock. Fingerprint cards are handled countless times and may be stored in files for many years. For these reasons, the texture and strength of the card must be such that it will withstand frequent handling.
In addition to the spaces for the fingerprint impressions, there is room on the card to record information about the person being printed (e.g., name, date of birth), information about the agency, and space for the date and signatures of the subject and technician.
Livescan technology replaces the process of using ink to record friction ridge detail. The friction ridge surfaces to be recorded are placed on a scanner that records the detail in a matter of seconds. High-resolution scanners can produce images that rival the quality of ink recordings, and the digital images are easily reproduced and distributed electronically. The process of rolling the finger impressions (and plain impressions) on the scanner platen is the same as for the actual recording of inked impressions on a card, but without the ink.
The basic method of recording friction ridge detail on the hands or feet can be accomplished by applying a thin coat of black ink directly to the skin’s surface using a roller or by coating an inking plate with the ink and rolling the fingers onto the plate. Next, the inked skin is pressed on a surface of contrasting color, such as a white piece of paper or a fingerprint card. The difference in elevation between the ridges and the furrows of the friction ridge skin leaves a print that is a recording of the unique detail of the friction ridge skin.
To begin this process, if using the ink-and-roller method, a small amount of ink is deposited at the edge, center, and opposite edge of a thoroughly cleaned inking plate. The ink is then rolled and smoothed out. The ink should look black, not gray. A gray color means that there is not enough ink on the plate. The ink should not look wet. If the ink looks wet, too much ink has been placed on the plate, and this could result in a smearing of the print. After the proper amount of ink has been rolled onto the plate, the next step is to ink the fingers.
Before any ink is applied to the fingers, the fingers must be inspected to ensure that they are clean and dry, because contaminants can interfere with proper recording. If the subject’s fingers are too dry, a moisturizing hand lotion may be applied sparingly to soften the fingers. If the subject’s fingers are too moist, they must be dried individually or, in case of excess moisture, wiped with an alcohol wipe and then dried. Regardless of what method of recording is used (ink and roller, Porelon Pad, or scanning device), the fingers should be rolled away from the body, and the thumbs should be rolled toward the body (thumbs in, fingers out). This procedure allows the fingers and thumbs to be rolled from an awkward position to a more relaxed position and is less likely to produce smeared recordings.
To completely roll each finger, with the subject standing in front of and facing the cardholder, the hand should be firmly grasped in such a manner that the finger is extended and the other fingers are out of the way. The inking plate and the cardholder should be side by side, with the cardholder nearest the operator. The hand is then rotated so that the side of the finger can be placed on the inking plate. While one of the operator’s hands grasps the hand of the subject, the operator’s other hand holds the end of the finger or thumb being printed to keep it from slipping, to apply light pressure, and to guide the roll.
Two key factors to remember are control and pressure. For best results, the subject should not help with the process and should be asked to remain in a relaxed posture. The finger or thumb is then rotated 180° (i.e., nail edge to nail edge) and is immediately lifted from the plate and rolled in the same manner in the appropriate box on the fingerprint card that has been previously placed in the cardholder.
The plain (i.e., flat or simultaneous) impressions are recorded by grouping the fingers from each hand and pressing them on the inking plate. The grouped fingers, numbers 2–5 and 7–10, are then pressed on the fingerprint card or scanning device in the appropriate boxes, taking care not to superimpose these impressions over the rolled impressions. The thumbs are inked and recorded separately in the same manner. The fingers and thumbs that are recorded in these boxes should not be rolled from side to side. As the fingers and thumbs are lifted from the card or scanning device, they should be rolled toward the tips of the fingers by keeping pressure on the fingers and lifting the subject’s wrists so as to record as much friction ridge detail as possible toward the top of the pattern area.
Palmprints are recorded in much the same manner as fingerprints; however, a cylindrical device is often used to facilitate the process to ensure complete recording of all friction ridge detail. The palms are not pressed on an inking plate. Rather, the roller is loaded with ink from the inking plate and the ink roller is used to apply a thin coat of ink directly to the hands from the base and edges of the palms to the tips of the fingers. Care must be exercised to ensure complete coverage of ink to all areas containing friction ridge detail.
To record palmprints, a standard 8” x 8” card or heavy plain white bond paper is attached to a cylinder approximately 3” in diameter. Removable adhesive tape or rubber bands may be used to attach the paper to the cylinder. (Some technicians prefer to let the paper “ride” across the cylinder without attaching it, taking care to prevent slippage.) The inked palm is then rolled either from the base of the palm toward the fingers or from the fingers to the base of the palm. Either way is acceptable and is generally left to the discretion of the technician. Most technicians prefer beginning at the base of the palm and rolling toward the fingers because this gives the technician more control over the subject and position of the print on the card.
The hand can simply be pulled rather than pushed across the surface, which also tends to help prevent lateral movement of the subject’s hand. The palm must be recorded in one smooth, unceasing motion to prevent smudging or distortion. Light pressure should also be applied while rolling in order to maintain completeness and to adequately record the centers of the palms. (Extending the thumb to the side will also help eliminate voids in the center of the recorded palm.) The thumbs are recorded separately because of their position on the hand. The extreme side of the palm, opposite of the thumb, referred to as the “writer’s palm” (i.e., the edge of the hypothenar area), is also recorded separately on the palmprint card. The card is removed from the cylinder and placed on a hard flat surface.
This area of the palm is then pressed on the palmprint card, with the little finger extended, to the right of the previously recorded palmprint for the right hand and to the left of the previously recorded palmprint for the left hand, if space allows. The thumb area of the palm (thenar area) is then recorded in the same manner and placed to the left side of the previously recorded right palmprint and to the right side of the previously recorded left palmprint, again, if space allows. If adequate space does not allow for the thenar and hypothenar areas to be recorded on the same card, separate cards should be used for these recordings.
Major case prints (also referred to as major criminal prints) are a recording of all the friction ridge detail covering the hands. If necessary, this may also include a recording of all the friction ridge detail on the feet. In addition to legible and completely recorded fingerprints and palmprints, major case prints include a legible and completely recorded set of the tips of the fingers, from just below the nail to the center of the fingers, rolled from one side of the nail to the other, as well as completely recorded lower joints of the fingers, including the extreme sides. Major case prints are often required for comparison to unknown impressions that have been collected from crime scenes, and these impressions may include areas of friction ridge detail that are not routinely recorded.
To begin, a complete set of the subject’s fingerprints should be recorded as previously described. Next, all of the remaining friction ridge detail on the phalangeal areas of the thumbs and fingers is recorded using 8” x 8” cards or white bond paper firmly attached to the edge of a table. Beginning with the right thumb, a thin coat of ink is applied to all of the friction ridge detail with an ink roller, from the base of the thumb to the tip, including the extreme sides of the finger. Usually beginning at the lower left corner of the paper, the extreme left side of the thumb is firmly pressed on the paper. The thumb is removed by lifting from the base of the thumb to the tip. This will record the extreme left side of the thumb and tip.
Next to this impression, the center of the thumb is placed on the paper and is removed in the same manner, thus completely recording the friction ridge detail from the base of the thumb to the tip. The extreme right side of the thumb is then placed to the right of the center portion, thus recording the extreme right side of the thumb and tip. Lastly, above the three recorded areas of the thumb, the extreme left side of the tip of the thumb is placed on the paper and rolled to the extreme right side with one continuous motion. This group of recorded friction ridge details of the thumb should be labeled “#1”, or “right thumb”, above the rolled tip (Figure 4–6). This process should be repeated with the remaining four fingers of the right hand, moving counterclockwise around the paper.
On occasion, it may become necessary to record a subject’s footprints. The same basic procedures as with recording palmprints are used; however, because of the large size of an adult foot, a larger cylinder and paper must be used. The cylinder used for this process should be approximately 5” in diameter and should hold an 8.5” x 14” (legal size) sheet of heavy white bond paper attached to the cylinder, as previously described. The foot should be rolled across the paper in the same manner as the palmprints, in one smooth, continuous motion from the heel of the foot toward the toe, with the toes passing completely over the cylinder.
Recordings of the feet may also be obtained by applying ink to the bottoms of the subject’s feet with a roller and instructing the subject to walk across paper that has been laid out on the floor. This, however, requires cooperation from the subject and may not produce satisfactory recordings, because excessive pressure and movement of the feet may blur or smear the impressions. Another method is to mount a card or paper on a flat board. With the subject in a sitting position and with the leg elevated and supported, the paper is pressed against the subject’s inked foot.
Recording Prints From A Deceased Person
Coordinate with the Medical Examiner or Coroner before attempting to collect prints from a deceased person. Protect a deceased person’s hands and feet by covering them with paper bags that are secured at the victim’s wrist and ankle. Never use plastic bags to protect these areas of a body. Elimination prints can be collected after evidence collection has occurred. The preferred method for collecting comparison/elimination prints is using ink. Finger, palm, hand, toe, heel, feet, and major case prints can be inked and rolled. Always use clean gloves when handling evidence.
Before collecting prints, ensure that the hands are photographed to document any trace material or physiological fluid which may be present, and collect the material before proceeding. Set up the location where prints will be taken, preferably on a flat surface. Ensure that fingerprint supplies are easily accessible and ready for use. Instruct the person to clean their hands before rolling the prints if applicable. Complete as much of the information requested on the print card as possible. Critical information includes your name and identification number, the name of the fingerprinted person, the date and time, and which hand was printed. Insert the print card into a cardholder.
Position the person being printed so that the hands are easily accessible to you without your firearm side being exposed if you are wearing a firearm. Just before rolling prints, put on clean gloves to ensure that you have eliminated the possibility of transferring your prints to the card. The person being printed should stand facing the print card. You can stand, being sure to safeguard your firearm if you are wearing one, to the side of the hand being printed or in front of the person.
Hold the person’s thumb tip and wrist gently, and press the thumb onto the ink strip. Roll the thumb on the ink from the edge of the nail on one side to the edge of the nail on the other side. Be sure to ink the tip of the thumb (or finger) well so that the developed print is as clear and complete as possible. Gently and with steady force, press the inked thumb to the card and roll it from the edge of the nail on one side to the edge of the nail on the other side. Repeat the inking and rolling process for all fingers on one hand, starting with the index finger. Print the fingers in this order: index, middle, ring, and little.
When a print is smudged or otherwise defective on the card, take another print on a new card for that finger only. Label the card so that it clearly corresponds with the card containing the smudged print. Never discard a print card; do not cover the print with a fingerprint tab designed for this purpose. When print impressions are not clear due to a skin condition or other circumstance, write “Best print possible due to (reason)” in the space nearest the print on the card. When a finger is injured or missing, note the condition in the space for that finger. When necessary, obtain a new card for the prints from the other hand. When using a ten-print card, use the space provided for the other hand. Package to protect the completed card.
Finger, palm, hand, toe, heel, and feet prints, and major case prints can also be developed using this method. Always use clean gloves when handling evidence. Prepare to take the prints by setting up the location where prints will be taken and instructing the person to clean their hands if they are very soiled. Before collecting prints, ensure that the hands are photographed to document any trace material or physiological fluid which may be present, and collect the material before proceeding. Complete as much of the information requested on the print card as possible. Critical information includes your name and identification number, the name of the fingerprinted person, the date and time, and which hand was printed. Avoid touching the lifter in the area where the person’s prints will be developed.
Cut a sheet of flexible plastic lifter into 1½”×8″ strips to record fingers. Rub a small amount of fingertip moistener onto the subject’s fingers. Any excess may be wiped off with a paper towel. Lightly dust palm side of the hand with black fingerprint powder. Separate release paper from the flexible plastic lifter. Spread fingers and press hand on the adhesive side of the lifter. Lift hand. Press the lifter along the length of each finger, and around the sides of the fingertips. Press around thumb as much as possible. Larger pieces of lifter can be used to capture palm detail.
Prepare a backing material, such as clear acetate, and cover the adhesive side of the lifter with the acetate. Write identifying information on the back of the lifter. Trim and add to a ten-print fingerprint card, if applicable. When print impressions are not clear due to a skin condition or other circumstance, write “Best print possible due to (reason).” in the space nearest the print on the card. When a thumb or finger is injured or missing, note the condition of the thumb or finger in the space for the print. Repeat the rolling and dusting process to collect the thumb and fingerprints from the person’s other hand. Place the print cards in the container.
References and Further Reading
Office of Justice Programs. (2018). Defining the Difficulty of Fingerprint Comparisons. Available: https://nij.gov/topics/forensics/evidence/impression/Pages/defining-difficulty-of-fingerprint-comparisons.aspx
Modification History File Created: 05/02/2019 Last Modified: 05/22/2019
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