The Science of Fingerprints Part 24

There is a wide choice of film which can be used for this purpose. The so-called soft films are all good for photographing ridge detail on fingers. Process film is not recommended inasmuch as the film presents too much of a contrast. Consequently, if it is used, some of the ridge detail will be lost, especially if wrinkles are present in the skin.

Lighting is accomplished by the use of gooseneck lamps, floodlights, or a spotlight. If a fingerprint camera is used, its lights may be sufficient.

The manner of lighting may be by direct light, side light, transmitted light or reflected light, depending upon the prevailing condition of the finger or skin.

Direct light is used in those cases in which the ridge detail is fairly clear and there are no wrinkles present; or, if wrinkles are present, they are not deep enough to interfere with photographing the ridges.

Side lighting is used when there are no wrinkles of any consequence and the ridge detail is clear but because of discoloration the ridges are not readily seen in the ground gla.s.s as there is lack of contrast between ridges and depressions. Accordingly, the lights, instead of being focused directly on the skin or finger, are placed to the side of the object so that the light is directed across the skin or finger, thus highlighting the ridges and shading the depressions.

In side lighting, two lights may be used. Better results are often obtained, however, by using only one light, such as a spotlight, the beam of which can be controlled to best advantage.

Transmitted light is used in cases in which the skin has peeled off or in which the dermis has been removed, cut, and sc.r.a.ped thin so that light will go through. The prepared skin is placed between two pieces of gla.s.s pressed together in order to flatten the skin or dermis and remove creases. By tr.i.m.m.i.n.g some of the surplus skin or dermis, especially at the top, it may be more easily flattened. After the gla.s.s is properly mounted in front of the camera, the lights are placed behind it and light is directed through the skin. The ridge detail is brought into focus on the ground gla.s.s. Before the picture is actually taken it is suggested that the ground gla.s.s be checked by first using one light and then two lights to see which is more effective.

There will be instances in which the second layer of skin, cut and sc.r.a.ped thin enough to flatten out, fails when dry to have a sufficient contrast between ridges and depressions for purposes of photographing. The same piece of skin when soaked in xylene will show a marked contrast, which it loses on drying. This difficulty is overcome by photographing the skin while in solution, which can be done by placing the skin in a test tube or a small bottle of a size to keep the skin upright and the ridges toward the camera. The test tube or bottle is then filled with xylene.

If the skin is sufficiently thin, transmitted light may be used.

Should it be found, however, that transmitted light is not effective, then direct light may be tried and the results checked in the ground gla.s.s (fig. 401).

When photographing a small curved surface such as a test tube, direct lighting will usually create a high light. If the high light as shown in the ground gla.s.s is over the ridge detail on the skin, a poor photograph will result. If the high light cannot be removed by rearranging the lights, then reflected light should be tried.

In order to effect reflected light a large piece of white paper, cardboard, or similar material is used. A hole is cut in the center of the paper or cardboard. This must be big enough for the camera lens to protrude through. The ends of the paper or board are curved toward the skin or finger to be photographed. The lamps which are to be used are placed facing the curved paper or cardboard in such fashion that the light will strike the paper or board and be reflected by the curved surface to the object.

The lamps should be close enough to the paper or board to give the maximum light. Care should be exercised, however, not to place them too close, because of the fire hazard.

Any arrangement of lamps and reflectors giving a similar effect as the above should prove suitable.

Fingers or skin which have a mottled, reddish-brown color because of decomposition, exposure to severe heat, or diffusion with blood present a problem of lack of contrast between ridges and depressions for photographic purposes. This lack of contrast can be overcome to a large extent by the use of a yellow or light red filter. Sometimes, in those cases where the discoloration is due to the diffusion of blood throughout the tissues, the blood can be washed out by saturating and rinsing the specimen in a 10- to 20-percent solution of citric acid.

If, of course, the blood is not removed satisfactorily, the photographing should be done with the filter.

[Ill.u.s.tration: 401]

As previously stated, the fingerprint camera can be readily adapted to the use of photographing fingers or skin specimens for ridge detail.

Sometimes it is possible to photograph the skin or finger in the same manner as one does a latent print. There will be instances, however, in which the standard use of the fingerprint camera will not be possible or effective, such as for side light, reflected light, and sometimes transmitted light, or instances in which it is not possible to get the finger or skin flush with the opening of the camera. In these instances the lights of the camera are not used, so the batteries should be removed and gooseneck lamps or other suitable lighting equipment and ground gla.s.s utilized when the finger or skin is prepared for photographing (fig. 402).

The camera is opened either at the point where the lights are housed or at the lens point, whichever is most effective. Then, opening the shutter, the operator moves the camera either toward or away from the finger or skin to the point where the ridge detail is sharpest in the ground gla.s.s. The camera is held firmly, the ground gla.s.s is removed, the film is inserted and the photograph taken.

[Ill.u.s.tration: 402]

With respect to exposure time, it is possible only to generalize and point out that each case will have its own individual aspects.

Controlling features for consideration will be the type of film, the type and size of lights, the method of lighting (direct, side, transmitted or reflected) and also whether or not filters are used.

Accordingly, there may be a wide variation of exposure time in different cases.

The best approach for arriving at the proper exposure time is merely to make a test exposure, develop the film, and from an examination determine if it is underexposed or overexposed. Time the next exposure accordingly, until satisfactory results are obtained.

As has been mentioned previously, when photographing the ridges on fingers or skin, the ridge detail will be in reverse position, the opposite from an inked impression made from the same skin or finger.

(This is true except in those cases in which the underside of the epidermis is photographed.) Accordingly, when the negative is printed, it should be printed gloss side to sensitive side of paper to give the position comparable to an inked print made from the same skin or finger. In order to avoid error or confusion a notation should be made on the photograph of each finger, or, if they are cut and mounted on a fingerprint card, point out that the position has been reversed and that the prints are in their correct position for cla.s.sifying and searching. Otherwise, it is possible that the right hand may be mistaken for the left hand and vice versa.

If the underside of the epidermis or outer skin is being photographed, the negative should be printed in the normal manner, that is, emulsion side of negative to sensitized side of paper. Here, reversal of position is not necessary for when the ridge detail is viewed from the underside it appears to be in the same position as the inked impression normally is reflected on a fingerprint card.

Care should be taken to see that each photograph is labeled correctly to indicate the finger it represents, such as right thumb, right index, right ring, etc. It is imperative that no error occurs in such labeling, inasmuch as it is highly probable that the resultant cla.s.sification would be incorrect and failure to make an identification might very easily follow.

_Deceased infants_

The foregoing has dealt with the securing of fingerprints of unknown deceased persons for identification purposes. The basis for such action is the presumptive possibility that the unknowns had been fingerprinted previously and through this medium might be identified.

Another type of problem, however, arises with the finding of a deceased infant. It can be safely a.s.sumed that the possibility of there being in existence a set of known fingerprints of the infant is extremely remote. Nevertheless, in view of the fact that many hospitals throughout the country, as part of the general routine of recording a birth, secure the infant's footprints, it would follow that there could be a remote possibility of identifying the deceased infant through its footprints. The foregoing principles and procedures would then apply in securing the foot impression of a deceased infant.

It is fully realized that in practically all cases involving the finding of an abandoned infant corpse the infant is probably illegitimate issue and delivery did not occur in a hospital, but there have been instances where such was not the case.

The importance of securing footprints of deceased infants killed in a common disaster cannot be overemphasized. Such disasters may involve the death of infants of lawful issue, and in many instances there are hospital footprint records available which may prove of value as a positive means of identification.

_Technical consideration_

The methods described are intended to record, either by printing with ink or by photographing as legibly as possible, the ridge details of the tips of the fingers of unknown dead for identification purposes.

The securing of the impressions enables the fingerprint examiner to cla.s.sify and search them through a file. This "search," of course, means merely to make a comparison of the deceased's prints with the prints of known individuals.

It is well to bear in mind the fact that the dermis or epidermis may have undergone certain physical changes and that in order for the fingerprint examiner to make a proper comparison he must know the changes which can and do occur. Otherwise, he may fail to make an identification (fig. 403).

[Ill.u.s.tration: 403. Epidermis or outer layer of skin commencing to peel from dermis or second layer of skin, result of decomposition.]

Consider first the epidermis or outer layer of skin in cases of maceration (the skin is water soaked). There may be considerable swelling. The ridges become broader and are more distinct. An inked impression in such an instance may show a pattern larger in area than a print made from the same finger when the person was alive. Also, if the skin is on the finger but is loose, inking and rolling could distort the impression so that some of the ridge formations would seem to be in a different alignment from corresponding details in a print made during life. When decomposition commences, what are really solid ridges may be broken, giving rise to the possibility that there appear to be more characteristics than there actually are (figs. 404 and 405).

[Ill.u.s.tration: 404. Inked fingerprint made during life.]

[Ill.u.s.tration: 405. Inked impression of same finger of deceased showing effect of decomposition.]

The existence of wrinkles may also cause the impression to acquire an appearance of dissimilarity when compared with the original inked print.

With respect to cases of desiccation, there will probably be shrinkage, hence, the impressions made may appear smaller than in life and the ridges will be finer. In cases in which the epidermis has been lost and there remains only the dermis or second layer, there will usually be shrinkage with the same results. Here also, wrinkles, if present, may cause a difference in appearance from the normal print.

[Ill.u.s.tration: 406]

In addition to shrinkage and wrinkles in cases involving the second layer of skin, there is a radical change in the appearance of the ridges themselves. The second or dermal layer of skin is composed of what are called dermal papillae which have the appearance of minute blunt pegs or nipples. The dermal papillae are arranged in double rows (fig. 406). Each double row lies deep in a ridge of the surface or epidermal layer and presents the same variations of ridge characteristics as are on the outer layer of skin except that they are double. Accordingly, when the second layer of skin is printed or photographed, the ridge detail will appear in double. That is, the ridges will appear as though they were split. This may well confuse the fingerprint examiner in that what may be a loop having 10 ridge counts may appear to be a loop having 20 ridge counts when the impression is made from the second or dermal layer of skin. These double rows of ridges are finer and not as sharp as the detail on the outer skin, which adds to the difficulty of arriving at a correct cla.s.sification and making a proper comparison.

_FBI aid_

The above techniques and procedures have been dealt with upon the basis that the law enforcement officers would, when a corpse has been found, attempt to secure a set of finger impressions in an effort to identify the unknown dead. If, however, the officer feels that the job is too difficult or is beyond his scope, consideration should be given to cutting off the hands or fingers of the deceased and forwarding them to the Identification Division of the FBI for processing. If this course is decided upon, it is reiterated that local statutes governing the cutting of the dead must be complied with and proper authorization must be secured.

[Ill.u.s.tration: 407]

In order to facilitate the transmission of such specimens to the FBI the following suggestions are made:

First, it is deemed most desirable, when possible, to have both of the hands, severed at the wrist, forwarded in their entirety (fig. 407).

It is desired that the hands, rather than each separate finger, be sent inasmuch as it eliminates the possibility of getting the fingers mixed up or incorrectly labeled. If, however, it is not possible to send the hands for some reason, then, of course, the fingers should be cut off and forwarded. In cutting, the fingers should be cut off at the palm beginning with the right thumb, then the right index, ring, etc., just as though they were to be printed. As soon as each finger is cut off it should be placed in an individual container, such as a small gla.s.s jar, and immediately marked as to which particular finger it is.

In the event that the hands or fingers of more than one dead are being transmitted, it is absolutely necessary that not only the fingers be properly labeled but that each body also be given an identifying number or symbol which must be indicated on the hands or fingers cut from that body as well, in order to avoid the embarra.s.sing situation of identifying the hands and not knowing from which body they were cut.