The Science of Fingerprints, United States. Federal Bureau of Investigation [good books to read in english TXT] 📗

the articles on a piece of fiber board or plywood. The board should then be secured in a box so that the objects will not touch or be shaken against the sides in transit. The package should be plainly marked "Evidence," to prevent inadvertent handling on opening. Cotton or cloth should never be placed in direct contact with any surface bearing latent prints.

Any number of paper or cardboard specimens may be placed in a single protective wrapper, since contact with other surfaces does not harm latents on such objects. Lifts, negatives and photographs are readily enclosed with letters.

An explanatory letter should accompany all evidence. If it is necessary to pack the evidence separately, a copy of the letter should be placed in every package so that the recipient will know immediately the import of the contents. All items of evidence should be marked and described exactly in the accompanying letter so that they will not be confused with packing material of a similar nature, and to provide a check on what the package should contain.

In addition, the letter should include for record purposes a brief outline of the crime, i.e., type, date and place of occurrence, and names of victims and subjects. If suspects are named for comparison, sufficient descriptive data should be set out to permit location of their fingerprint records. This information, in preferential order, comprises the individual's complete name, aliases, FBI number, date of prior arrest or fingerprinting, fingerprint classification, date and place of birth, and physical description.

Evidence is preferably forwarded by registered mail or railway express, as these means provide records of dispatch and receipt.

Elimination or suspect fingerprints are best enclosed with the evidence itself, with a notation as to the type of prints forwarded.

CHAPTER XIII Powdering and Lifting Latent Impressions

 

The sole purpose in "developing" a latent impression is to make it visible so that it may be preserved and compared. Various powders and chemicals are used for this purpose. When a latent print is plainly visible, it should be photographed before any effort is made to develop it.

No attempt should be made to brush or apply powder to prints in dust, obviously greasy prints, or bloody prints, as this will almost surely destroy them. Objects which have been wet or immersed in water may still bear identifiable latent impressions. Before any examination is attempted, however, the object must be dried.

Powder brushed lightly over a latent-bearing surface will cling to grease or moisture in the ridges of a latent print, making it visible against the background. Obviously, a powder should be used which will contrast with the color of the surface. Photographic contrasts should also be considered.

A gray powder and a black powder are adequate for latent print work. Many fingerprint powders of various colors and compositions are available from fingerprint supply houses but none are superior to the gray and black.

A very small amount of powder is placed on the brush for application to the surface. Once the contour of a print is visible, the brush strokes should conform to the direction of the ridges. All excess powder should be brushed from between the ridges. Too much powder and too little brushing are the chief faults of beginners.

Gray powder is used on dark-colored surfaces. It is also used on mirrors and metal surfaces which have been polished to a mirrorlike finish, since these surfaces will photograph black with the fingerprint camera.

Black powder should be applied to white or light-colored surfaces.

Aluminum powder affords the same contrast as the gray. Gold and red bronze powders, although of a glittering appearance, will photograph dark and should consequently be used on light-colored surfaces. Dragon's blood powder is a photographically neutral powder and may be dusted on either a light or dark surface.

On clear transparent glass, either gray or black powder may be used, it being necessary only to use a contrasting black or white background when photographing.

Prints should be lifted after photographing. Both rubber and transparent tape are available for this purpose. Rubber lifting tape is procurable in black or white 4" x 9" sheets and has the adhesive surface protected with a celluloid cover. A black powder print should obviously be lifted on white tape and a gray powder print on black tape.

Gold bronze and red bronze powders should be lifted on white tape, aluminum on black. Dragon's blood may be lifted on either black or white.

After cutting a piece of tape sufficiently large to cover the entire latent print, the celluloid covering is removed and the adhesive side applied to the latent. The tape should be pressed evenly and firmly to the surface, taking care not to shift its position. It is then peeled gently from the surface and the piece of celluloid placed over the print to protect it. The operator should handle the lift in such a manner that he will leave no prints of his own on the adhesive surface. A small paper identification tag bearing the initials of the operator, date, and object from which lifted should be placed under one corner of the celluloid, or this information may be written on the back of the lift itself if it can be done in a permanent, legible manner.

If an excessive amount of powder adheres to the latent print, a more legible print may sometimes be obtained by lifting a second time (on a new piece of tape, of course).

It should be noted that a print lifted on rubber tape is in a reverse position. Consequently, in preparing a photograph of a print on such a lift, it will be necessary to print the negative from the reverse side in order for the print to appear in its correct position for comparison. Preparation of such photographs should not be attempted by persons of inadequate knowledge and experience.

Transparent tape with a durable adhesive surface is available in 1" to 2" widths for fingerprint work. The common variety of transparent tape is not suitable due to the deterioration (drying) of the adhesive surface. The print on a piece of transparent tape is in correct position. Transparent lifts should be affixed to a smooth, grainless, opaque background of a black or white color contrasting with the powder used. Every effort should be made to avoid air bubbles under such lifts. In no instance should a transparent lift ever be folded back on itself or stuck to another piece of such tape as a backing, since it is generally not possible to determine the correct position of such a print.

Groups of latent impressions, such as those of adjacent fingers or fingers and palms which appear to have been made simultaneously, should be lifted as units, that is, on a single piece of tape, as this may facilitate the task of making comparisons.

CHAPTER XIV Chemical Development of Latent Impressions

 

Chemical treatment in the development of latent finger impressions on paper, cardboard, and newly finished or unpainted wood may involve a slightly more complicated technique than that in which powders are utilized, but the results justify the additional effort.

It is very strongly recommended that powders not be applied to articles of the above types. This recommendation is made for several reasons. First, powders cannot be removed from paper and possibly may interfere with some types of document examinations. In this connection, they are likely to prevent restoration of the specimen to a legible condition. Powders will not develop as many latent impressions as chemicals on paper or cardboard. In some cases they will obscure latent impressions subsequently developed chemically.

Neither scientific training nor complete knowledge of the chemical processes involved is necessary for one to become proficient in the use of chemical developers, two of which will be discussed more fully. These two, iodine and silver nitrate, are the most commonly used, inasmuch as they are relatively inexpensive, readily procurable, effective, and easy to apply.

All specimens which are treated should be handled with tweezers or gloves.

When iodine crystals are subjected to a slight amount of heat they vaporize rapidly, producing violet fumes. These fumes are absorbed by fatty or oily matter with which they come in contact. If the specimen treated bears latent impressions which contain oil or fat, the print is developed or made visible by the absorption of the iodine fumes and the ridges of the print appear yellowish-brown against the background.

Iodine prints are not permanent and begin to fade once the fuming is stopped. It is necessary, therefore, for the operator to have a camera ready to photograph the prints immediately.

Control of the fumes is achieved by using the crystals in an iodine gun or fuming cabinet. The iodine gun may be assembled by the individual examiner, by a druggist, or it may be purchased through a fingerprint supply house.

Material for making the iodine gun, as well as iodine crystals, may be procured from a chemical supply house or through a druggist. The gun itself consists essentially of two parts. One tube (the end of the gun through which the breath is blown) contains a drying agent such as calcium chloride, to remove moisture from the breath. Without this, the moisture from the breath and saliva would condense at the end of the gun, drip onto the specimen and cause stains which might prove indelible. The second tube contains a small amount of iodine crystals which are vaporized by the heat of the breath, augmented by the warmth of the hand cupped around the tube containing the iodine. This vapor is blown onto the specimen (fig. 420). Glass wool serves to hold the calcium chloride and iodine in place.

 

Fig. 420

[Fig. 420]

 

Due to the amount of physical exertion involved, the gun is generally limited to the examination of a few small specimens. Where a large number of specimens are to be treated, the fuming cabinet, a box-shaped wooden receptacle with a glass front and top permitting the operator to control the amount of fumes in the cabinet and observe the development of the latent impressions, is used (fig. 421). The fumes are generated by placing a small alcohol burner under an evaporating dish containing the iodine crystals. This is set in a hole cut in the bottom of the cabinet. As soon as the fumes begin to appear in sufficient amounts, the burner is removed. The specimens may be hung in the cabinet by wooden clothes pins fastened to a removable stick which is supported by wooden strips affixed near the top edges of the cabinet. The top of the cabinet is removable to permit access. Diagrams for the construction of the iodine gun or fuming cabinet will be furnished on request to members of the law enforcement profession.

 

Fig. 421

[Fig. 421]

 

Many specimens bear small, greasy areas which, in addition to any latent impressions of a greasy nature, will also appear yellowish-brown after exposure to iodine fumes. All these stains will eventually disappear if the specimen is placed in a current of air from a fan or vent. All latent impressions on an object will not be developed by the iodine process but only those containing fat or oil. Due to this fact and the fact that iodine evaporates from the surface, it is used prior to (it cannot be used afterward), and in conjunction with, the silver nitrate process.

No ill effects have been noted from contact with small amounts of iodine vapor but prolonged or excessive contact will produce irritation of the skin and respiratory passages. To prevent gradual loss of the chemical through evaporation and the corrosion of surrounding metal surfaces, iodine crystals should be kept in an airtight container when not being used.

The development of latent impressions with silver nitrate is dependent on the fact that the sodium chloride (the same substance as common table salt) present in the perspiration which forms the ridges in most latent impressions reacts with the silver