FINDING AND PROCESSING LATENT PRINTS

"Latent" prints are chance or unintentional prints found on items of evidence or at a crime scene. Some prints can be plainly seen. They are made by a finger coated with a foreign substance like blood, grease, or dirt. Some prints are "plastic impressions" imprinted in pliable substances like butter, candles, putty, and semidry paint. Other prints, invisible or barely visible to the eye, are made by the natural body secretions of the hands and fingers.

The visibility of latent prints depends on the physical condition of the person who left the print, on the surface of the object, and on the angle of reflection of the light by which they are viewed. The visibility of prints also depends on the time that has passed since they were placed, the amount of heat to which they have been exposed, and other factors. The amount of time they stay on an object is affected by atmospheric conditions, air currents, and humidity. But even when the object has been exposed to adverse conditions, it may be possible to obtain prints.

Attempts to obtain prints should be made in all cases. Smudges lacking ridge features may have foreign substances like grease or blood on them. Although not serviceable as latent prints, they may provide other trace evidence.

Photographing prints found at crime scenes can safeguard fingerprint evidence. Taking photographs before attempting to preserve prints can offset damage which can sometimes occur in the preservation process. The photographs are also useful in the preparation and presentation of fingerprint evidence. After photographing fingerprints found at a crime scene, an enlargement can be made at the crime lab. Enlargements can be very useful in studying a print and comparing it with other prints.

PRESERVING PRINTS

Prints made visible by a foreign substance on the fingers often need only be lifted with print lifting tape. Or if the prints are on a small object, the whole object may beheld as evidence. But latent prints made by just the normal secretions of the skin often have to be processed in a special way before they can be seen and preserved. The most common means is by powdering or chemical treatment. Prints needing dusting powder to develop should be photographed before lifting. Prints found in dust should be photographed and then lifted. They should not be powdered, as this will destroy them.

POWDERING

Fingerprint powders are supplied in field kits in several colors, but black and white are used the most. Choose the powder that best contrasts with the background. These commercial powders have been developed over many years. They are dependable and of the right composition.

Some fingerprint equipment includes fluorescent powders to develop latent prints on multicolored surfaces. These powders are not often found in issued kits. They require a source of ultraviolet light. Long-wave ultraviolet light should be used, as short-wave ultraviolet light is harmful to the eyes and skin. And you must wear protective goggles and clothing. The choice of powder depends on whether the latent print is developed for photographing or lifting. As latent prints are normally lifted, the use of ultraviolet powders is rare.

To preserve a print with powder, first check for a test print in the area selected. Lightly brush it with powder to see if any unseen latent print is actually present. Then the surface can be wiped clean and the test print made and processed.

Fingerprint powder can be applied with fiberglass, camel hair, and feather brushes. A magnetic wand is used with magnetic powder. A large piece of cotton can be used for developing latent prints over a large area.

Pour some of the powder out of the container onto a sheet of paper. Just touch the tips of the brush to the powder. Then shake off the excess powder. The key to proper print development is to use a small amount of powder and a delicate touch. Using a smooth stroke, guide the brush over the suspected area or over the barely visible print. Get enough ridge detail to see the direction of flow of the ridges. The brushing, if continued, should follow the ridge flow. When the ridge detail is complete, photograph it. After the photograph you may use more powder to make the print more visible. Then photograph it again. Protect the print with lifting tape before sending it to the lab.

Sometimes the powder sticks to the object on which the print is found. If brushing will not remove the excess powder, make two lifts. The first lift will remove the excess powder. The second will preserve the fingerprint for identification needs. A latent print may be enhanced after the first lift by added processing with brush and powder.

If you are in the field without proper powders, you can use soot as a field expedient. Pass nonflammable objects through the smoke of a burning piece of pine wood or a wad of masking tape. A black, even deposit of soot will form on the object. Careful brushing will often yield latent prints.

LIFTING

The most common means used to lift latent prints are rubber lifters and transparent lifting tapes. Rubber lifters are better than transparent lifting tape for taking prints from curved or uneven surfaces. Transparent lifting tape has the advantage of presenting the lifted fingerprints in the correct position; the print is reversed on the rubber tape. Both tapes and lifters are available through General Services Administration supply sources. Ordinary transparent tapes used in homes and offices is not really suitable for lifting fingerprints. However, these tapes may be used as a field expedient. Other lifting materials are also available. White and black opaque lifting tapes are applied like rubber lifters. Hinged lifters with transparent tape and white and black backings are used like lifting tape.

Rubber lifters store well and come in both black and white for use with different colored powders. They are well suited to use on surfaces like doorknobs. Use a lifter large enough to cover the print and leave lots of room. Remove the plastic cover of a rubber lifter with care in one steady movement. Any pause will result in a line being left on the lifter. In most cases, powder on a print will not stick to the line, thus ruining the print. Place the adhesive side of the lifter to the powdered print. Press it down evenly, then peel the lifter from the surface on one smooth, even motion. Place the plastic cover of the lifter over the lifted print to protect it.

Using the transparent lifting tape available in dispensers speeds up the lifting process. Prints on transparent lifting tape should be mounted on material of a color that contrasts with that of the lifting powder.

When lifting a print with either manner, use care to halt air bubbles forming under the lifter. Keep a quarter twist on the tape with one hand while rolling it flat with the other to help prevent air bubbles.

CHEMICAL PROCESSING

All chemical processing of fingerprints is done at the laboratory. Lab technicians are trained to use many chemical mixtures to process the evidence. And they are trained to use the techniques required by federal regulations for the handling of dangerous, toxic chemicals.

Latent prints on paper products should be developed with chemicals. Paper acts as a blotter, absorbing skin secretions when touched. Thus, the latent prints will not rub off paper as they rub off a nonporous surface. The amount of contact and pressure by the fingers are the two variables that affect these latents the most. To develop the prints, the paper is exposed to chemicals that react with the skin secretions of the print residue. The chemical processes depend on the presence of mineral or organic matter in perspiration. Perspiration composition differs from person to person and from time to time in the same person. This difference accounts for the uncertain and frequently spotty development of these processes.

OBTAINING PRINTS OF LIVING PERSONS

Fingerprints impressions taken directly from a person's fingers for the purpose of identification must be uniformly clear and visible. It is not hard to take good, clear fingerprints. A good fingerprint impression is dark gray in color and free of smudges. All that is needed to obtain good prints is practice.

Have the subject sign the fingerprint card. It is not needed nor desired that you advise persons of their legal rights just to take their fingerprints. Have the subject wash his hands to remove any dirt particles. Make sure that the fingers are free of lint from the towels used to dry the hands. Gather your equipment together and ready it for printing.

In addition to fingerprint cards, you will need--

• A fingerprint card holder.
• Ink (printer's ink or any special fingerprint ink).
• A rubber ink roller.
• Plate glass (approximately 12" x 6" x l", fixed to a base).

Place a small dab of ink on the plate glass and roll until a thin, even film covers the surface. It helps to place a white card under the glass to check the ink's thickness while rolling it out and while inking fingers. Secure the fingerprint card in the holding device, and the equipment is ready to use.

The steps for inking fingers and the steps for making impressions on the card are the same. Each finger is rolled through the ink on the glass and then that finger impression is rolled on the fingerprint card. All rollings should be made in single movements. Do not roll back and forth. The pressure should be just enough to apply an even coat of ink on the finger and a clear image on the card.

After the procedure is complete, fill in the data on the fingerprint card. Sign the card or paper for identification. This signature is important in legal proceedings.

ROLLED IMPRESSIONS

Rolled impressions are made to show the entire friction surface of the finger or thumb, from the tip to one-fourth inch below the first joint. They are made by rolling the finger or thumb from nail edge to nail edge. This surface gives all the needed ridge characteristics for correct classification. (Classification is the means by which a set of fingerprints may be filed and then retrieved in the future.)

There is a specific means of rolling the subject's fingers or thumbs in the ink and on the fingerprint card to give a good impression. You roll the fingers or thumbs from "awkward to comfortable." To see what is meant, hold your hands in front of you with the backs of your hands together. Now roll them around so that the palms are together and thumbs are up. You will see that the right hand moved clockwise and the left hand counterclockwise. This is the direction the fingers on each hand should be moved. Thumbs are moved in the opposite direction of the fingers.

When you take prints, grasp the top of the subject's hand to make sure that the finger to be printed is extended. The roll is a single movement and with only enough pressure to give a clear print. Tell the subject to look away from the fingerprint card and to try not to "help" the roll. This will reduce smudging and give a clean impression.

PLAIN IMPRESSIONS

Plain impressions verify the order of the rolled impressions and show characteristics that are sometimes distorted in rolled prints. Plain impressions are made on the card by just pressing the four inked fingers on the card at a slight angle. They should show from the tips to one-fourth inch below the first joint. Thumbs are then printed by inking and pressing them on the block next to the plain finger impressions.

Have the subject hold his fingers straight and stiff. The h-and should be level with the wrist. Grasp the wrist with one hand and press the fingers onto the cards with the other hand. Then allow the subject to clean the ink from his fingers.

PALM PRINTS

You may need to obtain palm prints from a subject at times. This is because the whole hand makes a distinctive impression. These prints are sometimes found on evidence or at a crime scene. The biggest problem with making palm prints is that often the hollow part of the palm is not properly printed.

The best way to record palm prints is to have the printing paper wrapped around a tubular object. Place the heel or base of the subject's palm on the tubular object and roll the print in a pulling motion from the heel of the hand to the fingertips.

MAJOR CASE PRINTS

Major case prints are a complete set of prints. They include the record prints of inked finger, palm, and sole impressions taken for identification needs. And, in addition, they include edges of the hand, fingertips, and the entire finger. In effect, prints are made of all parts of the hand to include the tips, palm, sides of the fingers, and sides of the palm. Sometimes prints of the feet are also included. Major case prints often help in forgery cases. The print of the side of the hand leaves an impression like that of a hand in the writing position.

PROBLEM PRINTS

Excessive perspiration may cause inked impressions of many persons to blur. Wipe each finger with a cloth and then quickly ink and roll it on the fingerprint card. Follow this process with each finger. You may also wipe the fingers with alcohol or other drying agent. Some people have dry, rough hands from their work. Rubbing the tips of the fingers with oil or creams can often make them soft enough for clear, unsmudged prints. If the ridges are fine and small and the skin is soft, holding ice against the fingers sometimes helps.

If the hands and fingers are deformed, normal printing steps cannot be followed. Apply the ink directly to the fingers with a spatula or small roller. Then rotate a square piece of paper around the finger. When an acceptable print has been made, the square is taped to the proper box of the fingerprint card. If there is an extra finger (usually a "little" finger or a thumb), the innermost five are printed as usual on the card. The extra digit is then printed on the reverse of the card. Print webbed fingers as well as you can in the rolled and plain impressions. And if a finger or a fingertip is amputated, note that fact in the proper box. (Example: "AMP" 1st joint, FEB 1943 or "TIP AMP.")

OBTAINING PRINTS OF DECEASED PERSONS

Major case prints are always obtained of deceased persons connected with an investigation. The prints are used to identify or eliminate latent print evidence and to identify the deceased. When the body is in an Army mortuary in the graves registration system, graves registration can provide the major case prints.

Printing deceased persons may be done before rigor mortis has set in, after rigor mortis, or after decomposition has begun. The means used to take the prints depends on the conditions of the fingers and your ingenuity. The process of inking the fingers and rotating a square paper on the finger might be used. This works best with the recently dead or after rigor mortis is gone. When rigor mortis is present you may have to straighten the fingers. This can be accomplished by pressing down on the middle joint of the finger. You might dust the fingers and palms with fingerprint powder and lift the prints with tape or rubber lifters. This often works well to obtain difficult record prints. Be sure to mark each lift.

The hardest prints to obtain are those from a body which has begun to decompose. It may require techniques beyond your expertise, especially when the hands are badly charred or decomposed. In such cases, the hands or fingers should be sent to the laboratory for identification by laboratory personnel. But never send a portion of the body to the lab without first contacting the lab for guidance.

When needed, and with SJA advice, the hands or fingers may be amputated by a surgeon. Before amputation takes place, contact your USACIL to learn the best method of processing body parts. Put each body part in a separate bottle and be sure that each bottle is properly identified.

Latent Print evidence can typically be divided into two categories: Porous and Non-porous.

Porous evidence such as paper, unfinished wood, cardboard, etc., is normally conducive to the preservation of prints because latent print residue can soak into the surface.

Non-porous evidence such as plastic, glass, metal, foil, etc., is much more fragile because the latent print residue may just be lying on the surface. Even the slightest  handling can "wipe away" a latent print on non-porous surfaces.

Borderline or Questionable surfaces?  If you aren't sure whether a drop of water would soak into a surface... go ahead and treat it as non-porous.  You may otherwise "wipe-off" valuable latent prints during shipment to the lab.  Many latent prints are destroyed on shiny magazines and shiny cardboard cigarette cartons by failing to treat them as non-porous.

DO Submit all porous evidence to the laboratory for latent print processing. No "field processing" of this type evidence is required or desired.  Field expedient processes such as iodine fuming or dusting with magnetic powder should never be used.  They will fail to develop many latent prints and are far inferior to laboratory procedures.

DO Package porous evidence as conveniently as possible.  Wear gloves when handling the evidence.  Allow wet or damp evidence to dry before sealing and mailing to the lab.

DO wear gloves... but maybe not for the reasons you think!  Wear gloves primarily to keep your hands clean.  Assume that any relatively smooth area your gloves touch will destroy identifiable latent prints on non-porous or semi-porous surfaces.  When you are handling evidence without poison/drug or biohazard dangers, cloth gloves are more comfortable than surgical type gloves because your hands won't sweat.  Keep all gloves clean.  Touching a contaminated surface (such as scratching your oily nose) will result in fabric impressions from the gloves (or your own fingerprints when thin surgical gloves conform to your underlying friction skin ridges) later developing on the evidence... possibly obscuring an otherwise identifiable latent print from the perpetrator.  Clean gloves will not harm latent prints on papers or other porous surfaces.  If you keep cloth gloves just for handling evidence, keep several pairs so you can rotate and launder them routinely.  When you see investigators in the movies pick up a firearm or drinking glass with their hand covered by a handkerchief... you are seeing an example of how to almost certainly destroy the perpetrator's latent prints on those smooth, non-porous surfaces.

DO "Field process" all non-porous items by "super glue fuming" at the earliest possible time. Handle the evidence no more than necessary prior to the super glue process.

DO "Super glue fume" non-porous drug evidence items in almost all instances prior to packaging. All types of drug evidence can be super glue fumed prior to placing in a heat sealed evidence bag. (The chemical composition of the drug is not affected by super glue fumes.)

DO Submit all latent print lifts to the laboratory and allow latent print examiners to determine what lifts are suitable for identification.

DO Avoid unnecessary writing or marking on surfaces to be processed for latent prints. When possible use a pencil for marking porous items. Also avoid taping or sticking labels on the surfaces to be processed for latent prints.

DO Photograph all latent prints visible at the crime scene. Pay special attention to footwear impressions that may be in dust or dirt. Include a scale in all photographs.

DO Utilize an electrostatic dust print lifter to preserve footwear impressions found in dust or dirt on surfaces such as paper, floor tiles, walls, carpets, etc. (Collect the impression after photography.) Place each lift containing the impression in a separate box or container (such as clean pizza boxes or photo paper boxes). The lifts should be placed with the impression "face-up", taped on two edges then the lid should be closed and sealed to prevent the lift from attracting additional dust particles not related to the impression.

DO Utilize dental stone to obtain casts of footwear or tire impressions at the crime scene. Do not clean the casts, that will be done at the laboratory. Make sure the cast are completely dry then, package them securely to avoid breakage during shipment to the laboratory.

DO Photograph the footwear or tire impressions at the crime scene (90 degree angle with a scale, etc.) and forward the film to the laboratory along with any casts or dustprint foils obtained.

                                         Superglue Fuming

By NOT superglue fuming nonporous evidence before you mail it to the lab, you help the bad guys..... it's about the same as wiping the evidence clean.

Do NOT expect latent finger or palm prints on a pistol, knife, can, bottle, or credit card to survive mailing to the lab if you don't either:

A.  Superglue fume the evidence before mailing.

-or-

B.  Package the item in such a way that NOTHING can touch or rub against the smooth surfaces you want processed for latent prints.  If DNA testing of saliva on that beer bottle opening is important, wedge the bottle corner to corner in a sturdy cardboard box.  Next seal the box and place it inside another box with ample shock-absorbing plastic peanuts or other packing to prevent breakage during shipment.

When used with common sense, superglue fuming is a very safe technique used by police worldwide daily. The US Army has used superglue fuming since the late 1970's.

DO NOT USE A HOT PLATE. Use a coffee cup warmer or light bulb. The red-hot coils of a hot plate can cause a flash fire of the volatile superglue fumes, and the high temperature can release poisonous gases.

When you get the chance to, order a dozen one ounce containers of superglue through supply channels (for American military/federal supply sources, you can specify NSN# 8040-00-142-9193; MIL-A-46050C, Type II, CLS, 1 ounce).  This will save you money in the future. Don't order the one pound or one-liter containers because sometimes the lid becomes permanently glued on. Throwing away part of a one-ounce container is much better than wrestling with pliers and a large container of superglue that will stick your fingers together when the lid finally pops off.

Do not let the light bulb touch the walls of your cardboard chamber or your evidence, otherwise, you may start a fire.

Do your fuming in an area that is well ventilated. You will irritate your eyes and lungs if you do the fuming in a small office.

Your fire department can always provide a portable generator to power your heat source at important crime scenes. (They use the portable generators to power electric fans to clear out smoky air when a building's power is out. You can use their fans to clean out superglue fumes from an entire room if you fume the whole thing at once. Call the lab before fuming an entire room or vehicle.)

Use a fish aquarium as a chamber only if you enjoy cleaning off glass with lots of elbow grease periodically. If you don't clean off the inside of the aquarium, more and more of the superglue fumes will be wasted because the polymerization will occur on other superglue deposits before it will on relatively clean evidence. This will cause you to fume longer and use more liquid superglue. An alternative, if you already have an aquarium, is to line the interior with aluminum foil and replace the foil once a month or so. There is no need to watch the fuming while it is going on.

A cardboard box makes an excellent chamber, and you can throw it away and get another one once a month or so depending on how much white film deposits on the inside walls.

In a pinch, use a garbage can turned upside down, an old briefcase, etc., for a fuming chamber. A filing cabinet, with the drawers removed and a plastic bag taped over the front, works well for fuming M-16's. A locker with any vent slots covered over also works well for large items. Adjust your fuming time and amount of chemicals to accommodate the larger chamber space and larger surface area. Try twenty minutes for a large locker. Go longer if your test print didn't develop well.

There are a variety of non-heat source accelerated methods for superglue fuming evidence. Most involve applying the glue to plain cotton or cotton impregnated with chemicals. The superglue reacts with the cellulose and chemicals to create heat, and the resulting heat causes a portion of the superglue to fume. This is normally much slower and less efficient than using an electric heat source. If you do want to make some up, we suggest using merely a handful of clean sawdust mixed with a small amount of baking powder (optional). Tampons may be cut in half and used instead of sawdust or cotton.

Now available commercially are butane fueled miniature soldering torch fuming kits. These kits use steel wool impregnated with cyanoacrylate (and sometimes dyes).

CAUTION: Previous literature has reported release of deadly cyanide gas at temperatures as high as these mini-torch kits.

CAUTION NOTE:  This web page is a general guide for superglue fuming procedures before mailing evidence to a laboratory.  It explains the basics of how to superglue fume without expensive equipment such as a humidity chamber or vacuum chamber tailored for cyanoacrylate fuming.  At the U.S. Army Crime Lab we preach this information to investigators we support.  Investigators and Special Agents we serve generally do not hand carry evidence to our lab.

Before you start superglue fuming, be certain you know that the crime lab you submit evidence to desires such processing.  You could get your hand slapped by fingerprint experts at some laboratories because other very effective processing methods are available for processing nonporous evidence.  Many laboratories prefer vacuum metal deposition to superglue fuming, especially among European labs.  Also, some crime scene examination units (SOCO) utilize staining techniques on nonporous evidence in lieu of superglue fuming.

In making the decision to fume or just package to protect prints, you must sometimes decide which type of evidence has the greatest potential value:  finger/palm print identification of the suspect or other evidence such as paint chips, textile fibers, etc.  Recent research has shown that normal cyanoacrylate fuming (not an extreme, snow white over-developed layer) does not prohibit subsequent DNA exams of blood (but may inhibit DNA exam of saliva or semen).

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