The Science of Fingerprints Part 30

All fingerprint identifications are made by observing that two impressions have ridge characteristics of similar shapes which occupy the same relative positions in the patterns.

Methods involving superimposition of the prints are not recommended because such a procedure is possible only in a very few instances, due to the distortion of ridges in most prints through pressure and twisting. Such a procedure is not necessarily a test of ident.i.ty.

Likewise, presenting charts with the shapes of the characteristics drawn in the margin is not recommended. Individual ridge characteristics may vary slightly in actual shape or physical position due to twisting, pressure, incomplete inking, condition of latent print when developed, powder adhering to background, etc.

Identifications are based on a number of characteristics viewed in a unit relationship and not on the microscopic appearances of single characteristics.

Since the enlarged photographs appear in black and white, an ink other than black or white should be used to line the chart. Such an ink should be preferably translucent so that it will be possible to see the ridges which it traverses. A translucent carmine drawing ink serves well. In placing the lines on the chart, they should be arranged so that they do not cross or touch.

The chart will present a clearer, neater, and more pleasing appearance if it is numbered clockwise and the numbers are evenly s.p.a.ced (fig.

429). It is not necessary, however, to place the numbers evenly around the photograph.

[Ill.u.s.tration: 429. Chart ill.u.s.trating method of fingerprint identification.]

Ordinarily, the numbers are placed on three sides and the type of print (latent or ink) noted at the bottom. In any case, the manner of numbering should be subservient to an explanation of the characteristics in an orderly sequence; and, if the situation warrants it, all of the points may be ill.u.s.trated on a single side of the photograph.

A single line should be drawn from each characteristic to a numbered point on the margin. Care should be taken to draw the line exactly to the characteristic point, not short of it, beyond it, or obscuring it.

Erasures should be avoided. If the ink runs or blots, it is sometimes possible to remove it with a cloth dampened in denatured alcohol, without damaging the photograph.

If the enlargement is great, that is, 25 or 30 diameters, it might be well to draw a small circle around each characteristic and then draw the line from the circle to the number, since the ridge will be much thicker than the ill.u.s.trating line. All lines and numbers should be checked for absolute accuracy. The expert should also study the enlargements for _apparent discrepancies_ in the prints, which he might be called upon to explain.

The charted enlargements are readily mounted on stiff cardboard with rubber cement, which may be purchased in small tubes. After cementing the photograph to the cardboard, it should be placed under a heavy flat object which will cover the entire surface until dry to prevent warping and wrinkling. After drying, trim the two enlargements to the same square size with heavy scissors, a pen knife or scalpel, and fasten them together, book-fashion, with strips of the photographic tape used in blocking the negatives. Of course, if charts are large, 20 to 36 inches square, mounting is unnecessary and they will have to be supported in the courtroom with thumbtacks or metal rings.

Some courts do not permit numbering or lining of the photographs and the enlargements alone in these cases will have to suffice. If there is some question about admissibility of the charted enlargements, it is well to prepare an extra uncharted set.

CHAPTER XVII

_Unidentified Latent Fingerprint File_

From time to time the FBI is requested to conduct surveys and partic.i.p.ate in conferences and in police schools on the problem of fingerprint identification.

As a result of its observations in the course of these activities it has been found that many identification bureaus are not fully aware of the importance which latent finger impressions can have in connection with the ordinary handling of arrest fingerprint cards.

Many bureaus and departments spend considerable time in developing latent impressions in a particular case. If no immediate results are forthcoming, the latent impressions are filed for future reference.

Single fingerprint files have been maintained with success by some departments. Many others do not attempt to keep a file because of either limited personnel or lack of funds. In many departments, however, where such a file is maintained, too often latent impressions are simply filed with no regard to possible future use. Actually, these impressions should be treated as evidence directly connecting the subject with the crime.

Active consideration should be given to the latent impressions until they are identified or the case has been successfully prosecuted. It is definitely felt that the following suggested procedure might have some decided advantages.

It is suggested that in all cases where latent impressions are developed at the crime scene, or on an object used in connection with the commission of a crime, the impressions be properly photographed and lifted. The evidence, where possible and practicable, should be properly packed, labeled, and stored for future use in court (fig.

430).

Use care in wrapping the evidence to see that the latent impressions on the objects are not destroyed. If the specimens are later used in court, the impressions should still be clearly visible. In the same manner, all evidence not of a bulky nature, such as photographic negatives, photographs, and lifts of latent impressions, should be similarly preserved for future court use. It is to be emphasized that all material in one case should bear a case number. All specimens not of a bulky nature can be placed in an envelope and filed by this case number (fig. 431).

The above procedure is the usual one followed by the majority of identification bureaus in handling latent impressions. In order, however, to keep the latents in an active state, the photographs of all the latent impressions found in a particular case should be cut up and pasted on a 3 by 5 card bearing the case number and t.i.tle of the case (fig. 432).

[Ill.u.s.tration: 430. Evidence labeled and latents protected for storing for future court use.]

[Ill.u.s.tration: 431. Latent material in a case should be filed under a single case number.]

If numerous latents are developed, several cards should be used, all having the same number and t.i.tle. These cards are then filed by case number in a regular filing cabinet. Before this step is taken, every effort should be made to secure and compare the fingerprints of individuals who may legitimately have placed their prints on the objects which were examined. In addition, as part of the case report bearing the same case number as the latent impressions, there should be a notation pointing out that latent impressions were developed in the case and that they are on file.

[Ill.u.s.tration: 432. For ready current comparisons latents in a case are placed on a 3 x 5 card bearing case t.i.tle and number.]

Case #2345

Unknown Subjects Jones' Drug Co.

B&E 3-15-47

Fingerprint comparisons in this unidentified file can be made on the basis of fingerprints taken from day to day of individuals fingerprinted for criminal identification purposes. A routine may be set up whereby the fingerprints of individuals arrested each day will be compared the following day with the latent fingerprints filed in the unidentified latent file. It is most important that this procedure be rigidly followed from day to day. It is to be borne in mind that the comparisons are made whether the particular person is or is not a suspect in a certain case. Special attention should be paid to fingerprints of individuals charged with burglary, breaking and entering, armed robbery, and other similar crimes.

Should an identification be made of some latent prints, and others in the same case remain unidentified, the 3 by 5 card should remain in file until the case is fully closed, inasmuch as more than one person may be involved in the crime. Of course, if all the latents are identified, then the 3 by 5 card is removed and placed with the negatives, lifts, etc.

It may be deemed advisable to remove these latents from the file in instances where the statute of limitations covering the crime has run.

If the above procedure is rigidly followed, identification in many instances will result--more than would be effected if the department maintained only a single fingerprint file in which the latent prints were merely filed away. Very often such a latent fingerprint file is a source of information when all logical investigative leads have been exhausted.

_This resume of latent impressions has been prepared by the Federal Bureau of Investigation in the belief that it may be of possible interest to law enforcement officers desiring to avail themselves of latent identification evidence in connection with their investigative activities. It should be borne in mind that the comments and expressions set out in this book are not intended to convey the thought that the Federal Bureau of Investigation believes the points emphasized are the only ones of moment, or that other methods of developing latent impressions are not equally acceptable. The Federal Bureau of Investigation will be glad to answer any questions on the foregoing which may occur to any law enforcement officer who reads this material._