Fingerprinting Techniques

Fingerprinting techniques

means “You try it!” Do the activity wherever you see this symbol. . Background The current system of fingerprint analysis used by criminalists and law enforcement personnel originated with Sir Francis Galton in the 1880s. Galton had a wide range of interests and talents including psychology, meteorology, geography and genetics. This website (www.galton.org) gives a thorough introduction to this extraordinary person.

Once the idea of using fingerprints for identification purposes was proposed and accepted as being valid, the techniques for collecting and analyzing fingerprints naturally became more and more common and varied. There are currently dozens of ways of locating, highlighting, lifting and otherwise using fingerprints for identification purposes. Many of these techniques are employed for the purpose of solving criminal cases.

A fingerprint (or print from another part of the body such as the foot, the palm of the hand, or lips) involves a transfer of material from the body to an object. The material transferred may be a natural product of the person who made the print - such as water, salts, sweat, lipids, or blood – or some type of contaminant the person was exposed to – such as dyes, liquids, or powders. When taking a print directly from a person, such as when someone is arrested, a substance is applied to the fingers and then transferred to a piece of paper or other appropriate surface that enhances the fingerprint. These are sometimes called reference prints (or inked prints). At a crime scene, the person may have transferred natural materials or contaminants to a surface that leaves an identifiable print that can be linked to that individual. These are called latent prints since they are not readily obvious but can be detected by specialized means. For today’s exercise we will be taking reference prints and latent prints.

Important - General procedures: Proper technique is important so as not to disrupt the natural ridges that occur on the fingerprint that make identification possible. The finger should be rolled once onto the inkless compound from one side to the other. Then the finger is rolled once onto a suitable piece of paper. Never slide your finger across the surface.

In some inkless systems the paper used can be any type, but it must be heated in order to show the prints clearly. In other inkless systems there is a chemical reaction between the inkless compound and the paper, so it does not require heating. However, the paper used must be specially engineered with the right chemicals impregnated in it. Experiment with the techniques below by trying to make “inked” fingerprints on notebook paper (or any other type of paper).

Displaying your prints You can display your prints by simply taping them to a piece of typing paper with clear packing tape. Make sure that the print is dry before doing so. Label each print with the person’s name, the finger(s) used, and the technique used to make the print. Special Note This is a very messy lab because of all the powders used. Please clean up each station promptly before you leave to go to the next station. You will lose points if you leave a station without cleaning it first.

“ Reference” Prints Traditionally, reference prints involved applying a messy dye to the fingers. However, there are new techniques available that take advantage of chemical principles. For example, many “inked” prints are now done with inkless fingerprinting systems. A colorless, or nearly colorless, compound is applied to the fingers and then transferred to a suitable paper surface that chemically reacts with the compound. The result is virtually as good as a traditional inked print, but with a lot less mess!

- Experiment with the inkless fingerprinting systems. Follow any directions that are posted at the station. Each student should record one full set of prints in your report. LABEL EACH PRINT AS “ARCH, LOOP or WHORL”. If the print is not a good print, you do not have to redo it (to save the paper), but MAKE A NOTE of WHY IT IS A BAD PRINT (like “too dark”, or “not a full roll”).

Latent prints For the development of latent prints you often have to resort to more clever strategies. New systems are constantly being developed. You should experiment with all the techniques available until you are comfortable with each one. There are 3 powder-based systems. Follow the guidelines below when using any of the powders.

Important guidelines - Read these instructions before proceeding:

A. Making the print - You can make your own prints to practice the dusting and lifting techniques. Use a surface available at the station to make your print (such as a glass beaker or colorful tile). You may have to rub your finger along the side of your nose or behind your ear to pick up enough oil to make a good print. When making the print do not rub your finger across the surface or the ridges will smear together and the print will not be useful. Simply press your finger onto the surface, or roll it onto the surface.

B. Dusting the print – Use a powder which has a color that contrasts well with the surface where the print was made. During application, the tendency is to use too much powder. You should place a small amount of powder in a lid. Lightly tap the brush into the powder so that only the tip of the brush is getting powder on it. Lightly brush the powder onto the print in a circular motion. Do not press hard with the brush or you may smear the ridges which you hope to eventually see!

C. Lifting the print – You must be careful to place the tape so that it makes complete contact with the print. It is easy to get air bubbles under the tape. If you do, start over. There are 2 techniques commonly used to place the tape. One involves bending the tape in the middle, placing it on the print, and carefully rolling it outwards in opposite directions. The other technique is to start with one end of the tape stuck to the surface to the side of the print, and then carefully rolling it over the print. In either case, it can be tricky to avoid getting air bubbles under the tape. Attach all lifted prints to your report.  Practice your lifting technique on several different surfaces until you can achieve some proficiency. Your instructor can demonstrate these techniques.

1. Ninhydrin (DO THIS FIRST OR SECOND because a good print is needed for it to work well)– This compound reacts with amino acids to produce a purple product. Amino acids are used by your body to make proteins, so it stands to reason that your fingerprints may contain amino acids. However, if you have recently washed your hands there may not be many amino acids (this is why we are doing this technique first). This reaction normally takes about a day to fully develop. However, it can be sped up by using steam from a clothes iron.

 - Make a print on a piece of notebook paper. Dip the paper into the ninhydrin tray under the fume hood. Allow the paper to air dry briefly. Make sure that the iron is high on and that the steam is at its highest setting. Be careful handling the iron! Hover the iron over the paper so that the paper is exposed to the hot steam. Do not touch the paper with the iron. You should see the print develop as you’re steaming.

2. Silver nitrate – This technique takes advantage of the fact that your fingers secrete a small amount of salt (NaCl). Salt will react with silver nitrate (AgNO3) to produce visible products. The chemical reaction that occurs is similar to photography. With exposure to UV light, the print is “exposed” in a manner similar to photographic film being exposed. Prints produced in this manner may not be stable for a long period of time, so they should be photographed or scanned.

This technique can be modified for use on different types of material. For example, one of the silver nitrate solutions you will be testing is water based and the other is alcohol based. Experiment with both types.

 - Someone in your group should wear a glove for about 15 minutes prior to making the print. Choose the person in your group who has the strongest tendency towards sweating. When ready to make the print, remove the glove and make a set of prints on a piece of white notebook paper with all your fingers (be sure to press firmly and hold for a few seconds). Spray just enough of the silver nitrate to saturate the surface of the paper where the print is. Allow a few minutes to air dry. Take the print into a dark room and shine UV light on it until you see the print darken. This may take about 5 minutes or so. You can set the UV light on its side with the print next to it so that you don’t have to hold the light the whole time. 3. Contrasting Powder – This is the system which most people are familiar with because it is often used on television programs and it doesn’t involve any subtle chemical reactions. The powder simply sticks to the print and it can then be lifted using a clear tape.

 - Make a print on a glass object. Dust with a powder that will give a good contrast to the surface where the print is. For example, use a dark powder on glass objects, or a white powder if dusting for a print on the top of the lab bench.

4. Fluorescent powder – These powders are used when you suspect latent prints to be found on a multicolored surface. The rules are pretty much the same as for regular powders. However, special lighting is used to enhance the image.

 - Make a print on a multicolored surface. After applying the powder to the multicolored surface, take it into a dark room and view with UV lighting. You may then lift it with tape and attach it to your report.

5. Magnetic powder – This is fairly recent technology. The idea is the same as the other powders. However, the application is a little different. The “brush” is a magnet hidden inside a plastic cartridge. When the plunger is pushed in, the brush can be dipped in the magnetic powder. The iron filings will stick to the magnet and will act as the bristles of the brush. To remove the filings from the applicator, simply pull the plunger out while holding the iron filings over the powder container.

 - Make a print on a glass object. Load the magnetic brush with iron filings. Apply the iron filings to the fingerprint by brushing lightly across the surface of the print. The filings will come off and attach to the print. Then return any unused filings to the container. The print can now be lifted as usual.

6. Superglue fuming – Some prints can be difficult to find or are not pronounced enough to show well with a simple dusting technique (like those above). For example, if an investigator suspects there are prints on the inside of a car, it would be difficult to dust the entire inside surface of the car. Or the perpetrator was not kind enough to press his/her finger hard enough onto the surface when touching it. However, superglue fuming can be done to enhance a print. Then it can be dusted with the techniques described above to enhance even further.

One drawback of this technique is that the superglue is difficult to remove and it sticks to a lot of other potential physical evidence. So, if the inside of a car is to be fumed, it should first be examined for blood, DNA, hairs, fibers, etc before fuming.

The idea is rather simple. The superglue is first vaporized. This can be done with heat or by placing the superglue in contact with a cotton ball that has been soaked with NaOH (a strong base). The vapors can be noxious so this will be done in a sealed container. The vapors will then stick to the ridges from someone’s fingerprints and they will be more visible with the naked eye. Then they can be dusted and lifted using the same technique as used for the contrasting powders in step 3.

 - Make a print on a glass microscope slide or another object your instructor may have. Label the slide with your initials. Place the slide next to the fuming chamber in the fume hood. Your instructor will load all the slides from the class into the chamber at the same time. 7. Wetwop – This is a very recent technique that has been developed specifically for developing prints on tape. Duct tape is often used by criminals to tape someone’s mouth, tie someone’s hands, or bind other objects. When the tape is removed from the role the fingers will normally touch the sticky side of the tape. This is where the Wetwop is most effective.

 - Make a print by tearing off a piece of duct tape and touching your finger to the sticky part of the tape. Using the tray next to the common sink, brush some Wetwop compound onto the tape where the print is - use the camel hair brush provided (be conservative with the Wetwop compound). Wait for about 30 seconds and rinse with cool running water in the sink. To preserve the print apply a piece of clear tape to the print.

TO TURN IN:

Each pair:  1 sample print between the two of you for the following stations: Ninhydrin, Silver nitrate, Contrasting powders, Fluorescent powder, Magnetic powder, Superglue fuming,(MAYBE – your instructor will tell you) and Wetwop. Just tape your prints to a piece of notebook or printer paper.

Each Student  turn in a copy of his/her own reference prints labeled “arch, loop, or whorl”. If it is unable to be determined, there should still be a label by the print that describes WHY it is a bad print.

 His/her own answers to the following questions

Questions:

1. In your own words describe the difference between a visible print and a latent print.

2. What are reference prints and what are they used for?

OVER!!!! 3. True or False: When making reference prints, you should roll the finger back and forth to make sure it is a good print. Explain your answer.

4. What is the difference between a porous surface and a nonporous surface? Also give an example of each.

5. What technique for detecting latent prints do you believe would be most effective for

a) paper surfaces?

b) glass surfaces?

c) fabrics?

6. Include your reference prints by stapling or taping them here. Classify each as “arch, loop, or whorl”. If it is NOT a good print (if it would have to be re-done in real life), then comment on why (like “too dark”, “not a full roll” etc.)