The Science of Fingerprints Part 18

_Searching_

When searching a print through the fingerprint files in order to establish an identification, it should be remembered that the fingerprint cards are filed in such a way that all those prints having the same cla.s.sification are together. Thus, the print being searched is compared only with the groups having a comparable cla.s.sification, rather than with the whole file.

After locating the proper group cla.s.sification, the searcher should fix in his mind the one or two most outstanding characteristics of the patterns of the current print and look for them among the prints in file. If a print is found which has a characteristic resembling one upon the current print, the two prints should be examined closely to determine if identical. To avoid making an erroneous identification, the searcher should be exceedingly careful to ascertain that the prints being compared are identical in all respects before identifying one against the other.

To establish ident.i.ty, it is necessary to locate several points of ident.i.ty among the characteristics of the prints. The number of identical characteristics is left to the discretion of the individual but he should be absolutely certain that the prints are identical before treating them as such. Characteristics need not appear within the pattern area, since any ridge formation is acceptable. Quite often excellent ridge detail appears in the second joint of the finger. The characteristics used to establish an identification are shown in figure 102.

The final and the key may be considered control figures for searching prints. They limit the number of prints it is necessary to search in a group to those prints having finals and keys closely related to the final and key of the print being searched.

Due to the possibility of visual misinterpretation, distortion by pressure, or poor condition of the ridge detail of the prints in file, it is advisable to allow a margin for such discrepancies. Except in cases where the ridge count of the final and/or key is questionable on the print being searched, the following procedure is used:

Of the prints within any group cla.s.sification, only those prints are examined which have a final within 2 ridge counts on each side of the final of the print being searched. For example, if the print to be searched has a final of 17, all prints bearing a final 15 through 19 will be compared with it.

Within the final of any group cla.s.sification, only those prints are examined which have a key within 2 ridge counts on each side of the key of the print being searched. For example, if the print to be searched has a key of 20, all prints bearing a key of 18 through 22 will be compared with it.

In figure 352, it will be noted that there are 17 ridge counts appearing in the right little finger and this number is used as the final. It will also be noted that there is a loop of 24 ridge counts in the right thumb and this number is used as the key inasmuch as it is the first loop. In this example, the print is searched in the group cla.s.sification which has finals ranging from 15 through 19. Within this group of finals the prints which have keys ranging from 22 through 26 are examined.

_Referencing_

Too much stress cannot be placed upon the necessity of referencing questionable patterns, whether it be in the interpretation of the type of pattern, the ridge count, or the tracing.

The factors which make it necessary are: variation in individual judgment and eyesight, the amount of ink used, the amount of pressure used in taking the prints, the difference in width of the rolled impressions, skin diseases, worn ridges due to age or occupations, temporary and permanent scars, bandaged fingers, crippled hands, and amputation.

_For the highest degree of accuracy, all rolled impressions should be checked by the plain impressions_, which generally are not distorted by pressure. This also helps prevent error caused by the reversal or mixing of the rolled impressions out of their proper order. For the same reason, as much of the counting and tracing should be done in the plain impressions as it is possible to do.

If there is any doubt as to which of two or more cla.s.sifications should be a.s.signed to a given pattern, it is given the preferred cla.s.sification and reference searches are conducted in all other possible cla.s.sifications. For example, if on a print with the preferred cla.s.sification

1 A ---- 1 Aa

it is questionable whether the left middle finger should be a plain arch, a tented arch, or a radial loop, the print is searched in the

1 A ---- 1 Aa

group, and reference searches are conducted in the

1 A ---- 1 At

and

1 A ---- 1 Ar

groups. For further ill.u.s.tration, a print is given a preferred primary cla.s.sification of

1, - 1

although the ridge detail on the right thumb is so formed as to resemble a whorl. The search is completed first in the preferred

1 - 1

primary cla.s.sification and a reference search is then conducted in the

1 -- 17

primary.

All ridge counts that are "line counts," i.e., when one more or one less count would change the designation of the loop from I to O or from S to M, etc., must be searched in both groups. For example, in a print cla.s.sified

16 M 1 U III 10, --------------- M 1 U III

if the ridge count of the right middle finger is 10 and the count in the right thumb is 16 (as indicated by the key), the print would be searched first as cla.s.sified, then reference searches would be conducted in the following groups:

M 1 U IOI, L 1 U III, L 1 U IOI --------- --------- and --------- M 1 U III M 1 U III M 1 U III

When there is doubt concerning the tracing of a whorl, it should be treated in the same fashion. For example, if in the cla.s.sification

O 5 U ------ I 17 U

doubt existed as to whether the tracing of the right thumb might not be a meeting tracing, the print would be searched as cla.s.sified, and a reference search would be conducted in

M 5 U.

------ I 17 U

If there is no doubt concerning the ridge count used for the final, it is enough to search out of the group only those prints containing a final within 2 ridge counts on each side of the final on the print being searched. When, however, there is doubt concerning the ridge count of the final, the print should be searched 2 ridge counts on each side of the two extremes of possibility. For example, if it were possible for a final to be 6, 7, 8, or 9 ridge counts, the print should be searched through that part of the group bearing finals of from 4 through 11.

The above explanation pertaining to the final also applies to the key.

All prints bearing amputations should be referenced to the necessary files containing prints other than amputations for reference searches.

In instances where only one finger is amputated, reference searches are conducted in all possible cla.s.sifications, including all possible ridge counts or tracings. For example, a print containing the cla.s.sification:

AMP

4 S 1 U III 6 ------------- S 1 U III

with the right index finger amputated, the left index finger being an ulnar loop, would be searched first in the amputation group for the cla.s.sification, then reference searches would be conducted in the following groups in the nonamputation files:

S 1 U III S 1 T II S 17 W III --------- --------- ---------- S 1 U III S 1 U III S 1 U III

S 1 U OII S 1 R III S 17 W MII --------- --------- ---------- S 1 U III S 1 U III S 1 U III

S 1 A II S 1 R OII S 17 W OII --------- --------- ---------- S 1 U III S 1 U III S 1 U III

All prints bearing unprinted or badly crippled fingers are filed in the nonamputation files, and reference searches are conducted in the amputation group.

For the purpose of determining if it is feasible to conduct reference searches in all possible cla.s.sifications, the method of referencing amputations is applied to completely scarred patterns (Chapter t.i.tled "Scarred Patterns--Amputations--Missing at Birth"). For example, a print bearing the preferred cla.s.sification:

13 O 17 W OOO 14 ---------------- L 17 U OOI