CHAPTER XII
_Latent Impressions_
Each ridge of the fingers, palms, and soles bears a row of sweat pores which in the average person constantly exude perspiration. Also, the ridges of the fingers and palms are in intermittent contact with other parts of the body, such as the hair and face, and with various objects, which may leave a film of grease or moisture on the ridges.
In touching an object, the film of moisture and/or grease may be transferred to the object, thus leaving an outline of the ridges of the fingers or palm thereon. This print is called a latent impression, the word "latent" meaning hidden, that is, the print many times is not readily visible.
Latent impressions, regardless of the area of the ridges present, are of the greatest importance to the criminal investigator as identification of them may solve the crime and result in successful prosecution of the subject. Consequently, every effort should be made to preserve and _identify_ them.
Visible prints in mediums such as blood, grease, dirt, or dust are equally important to the investigator but, strictly speaking, are not latent impressions.
A search of the crime scene should be conducted in a logical manner.
Points of entry and exit should be examined, along with surfaces or objects disturbed or likely touched during the commission of the crime. The examiner should wear a pair of light cloth gloves and handle an object only insofar as is necessary and then only by edges or surfaces which are not receptive to latent impressions. A record of the exact location of a print on an object and of the object itself should be made, since these facts may be of the utmost importance in any trial resulting from the investigation. No one should handle an object other than the examiner himself.
Portable articles removed should be labeled or marked so that they may be readily identified thereafter.
The beam of a flashlight played over the surface of an object will frequently show the location of latent impressions, although this is not an infallible test for their presence.
Evidence should be examined as soon as feasible after its discovery.
Following the location of any latent prints at the scene of a crime, the prints of all persons whose presence at the place under inspection has been for legitimate purposes must be excluded from further attention. It is advisable, therefore, during the initial stages of an investigation where latent prints are found, to secure the inked prints of all members of the household, the employees, and any police or other officials who may have touched the objects on which the latent impressions were found. Inked prints taken for this purpose are referred to as elimination prints.
Due to the fragmentary nature of most latent prints it is not possible to derive a cla.s.sification which makes a file search practicable. A latent impression may be identified, however, by comparison with the prints of a particular suspect.
Inked fingerprints taken for comparison with latent impressions should be as legible and as complete as possible, including the areas not essential to cla.s.sification, since identifications are often made with these areas. Inked palm prints taken should likewise be complete and clear and should include impressions of the finger joints. Persons not experienced in latent print comparisons should not attempt to evaluate latent fragments, since the area necessary for an identification may be extremely small compared to that of an average inked fingerprint.
Articles which are to be transported by mail or express should be so packed that the surfaces bearing latent impressions are not in contact with other surfaces. This may be accomplished by mounting 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 cla.s.sification, 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 b.l.o.o.d.y 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 gla.s.s, 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 doc.u.ment 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.