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Monday, November 12, 2007

The purpose of the Detail is to help keep you informed of the current state of affairs in the latent print community, to provide an avenue to circulate original fingerprint-related articles, and to announce important events as they happen in our field.
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compiled by Jon Stimac

Forensic experts swap tips from the field Deseret News, UT - Nov 7, 2007 "...Utah is hosting an "education conference" of specialists from a variety of forensic disciplines."

Meredith Friends' 'Indications of Guilt' Sky News, United Kingdom - Nov 11, 2007 “...a fingerprint found on Miss Kercher's face suggests that Knox held her down as she was attacked.”

Hunt for fourth suspect in Meredith murder, United Kingdom - Nov 11, 2007 "The manhunt for the fourth man was launched after forensic scientists identified a bloodied fingerprint on a cushion in the house where Miss Kercher died..."

Trial set in hitchhiker kidnap case The Union of Grass Valley, CA - Nov 9, 2007  "Latent fingerprint expert Linda Senteney of the state Department of Justice testified Thursday she found Sullivan's fingerprints on the water bottle..."

Recent CLPEX Posting Activity
Last Week's Board topics containing new posts
Moderated by Steve Everist

Baltimore Judge declares Fingerprints not reliable.
Justice Pie 2056 Sat Nov 10, 2007 1:25 am

Norberto Rivera 354 Sat Nov 10, 2007 1:06 am

Stitched vs Singular Live Scan Palm Images
Boyd Baumgartner 1639 Thu Nov 08, 2007 11:45 pm

Randall's Post from the Maryland Thread
Steve Everist 140 Thu Nov 08, 2007 4:26 pm

Looking for a fingerprint presentation for youth.
Anonymous 495 Thu Nov 08, 2007 3:33 pm

Latent Print Examiner Positions - CONUS/OCONUS
wkpetroka 4471 Mon Nov 05, 2007 12:28 am



Updated the Fingerprint Interest Group web page with FIG # 21.


Last week

we continued a 3-part historical series on the rarity of features in friction ridge identification.

This week

we continue with part 3 of the series.

The Reference Shelf (Gupta Discussion)
by J. Hess
LAPD Latent Finger Print Section

Our last two columns dealt with attempts to give some ridge characteristics greater value than others for the purpose of establishing identity of finger prints. The idea comes from the observation that ridge endings and bifurcations occur more often than other points. The article selected for discussion in this issue deals with a survey printed in the May, 1968, issue of International Criminal Police Review. The author, Sia Ram Gupta, calls it “Statistical Survey of Ridge Characteristics.” Mr. Gupta is a lecturer, researcher and an instructor at the Central Police School, Mt. Abu, India. His survey attempts to prove statistically that some characteristics are encountered fewer times than others; thus they should bear more weight in establishing identity.

Requirements Vary Greatly
In his introduction he points out the wide variation between different agencies in the number of characteristics considered necessary for positive identification of finger prints. Of course for the purpose of this series of articles, we are speaking primarily of latent prints where only a limited portion of the print is available for study. Even in India, the author’s home territory, the minimums vary from state to state. And because around the world the minimum number of points varies from six to 17, he feels it may undermine the court’s respect for the expert’s opinion. He reasons that the answer must be worldwide agreement among experts, based on statistical surveys and research that would provide a scientific background for the decision. The author cites the work of Senor Santamaria as an effort along these lines. (But note that when presented to the Interpol conference in 1953 they took no action.) Our column last month covered Santamaria’s survey.

IAI Is Studying The Matter
It is interesting to note here that the International Association for Identification resolved to have a committee report before its 56th annual conference in July of this year on what the association could consider a minimum number of points for a valid identification. Paul McCann and his committee have a tough assignment ahead of them, and the decision of this group will be carefully watched by members and non-members alike around the globe.

But, getting back to Gupta’s survey, it is concerned with the weight given to individual points in order to arrive at an acceptable minimum figure.

In looking into the details of the survey we see that the results were similar to Santamaria’s conclusions, with some differences in the mechanics.

Twelve ridge characteristics were considered. These were described as : (1) ridge ends terminating counter clockwise; (2) bifurcations; (3) lakes; (4) hooks; (5) dots; (6) short ridges; (7) whorls; (8) interchanges; (9) ridge ends terminating clockwise; (10) discontinuous ridges; (11) divergences; and (12) crossings.

These characteristics are illustrated in the article, thus agencies using different names for the same points can relate them to their terms.

How The Survey Was Made
The survey team took 1,000 standard finger print cards and from each card studied an ulnar loop from the left hand. This print was circled and then searched for a point of identity to use. Its type, relative position, and ridge count between it and the core or delta were considered. Here is an example of how the statistics were compiled.

A hook with the open end on the right of the ridge, opening upwards, was found on a print circled for study. It was separated from the core by four intervening ridges. Then all the prints on the 1,000 cards were searched for this same type of hook. It must be on the same level in relation to the core, and with four ridges intervening. From these statistics a percentage figure evolved indicating this combination could be expected to occur at a rate of 2%. In other words, two prints out of every 100 might have a hook of the same type and location. This same procedure was followed for each of the 12 different types of characteristics mentioned.

As expected, ridge endings and bifurcations had the highest duplication ratio, amounting to about 10% each. A table was compiled for each type of characteristic, and using these figures the author separated the 12 points into two groups, “common” and “uncommon.” The ratio shown by the table shows that the “common” points occur about ten times as often as those in the “uncommon” status.

Reasoning along the line that there will be about ten “common” points to every “uncommon” one in a print, and then the latter should be ten times more important than the former. Once this working ratio was established, he moved on to the next question.

Establishes Minimum Number
The next step was to set up a safe minimum number of points for a positive identification. Mr. Gupta estimated the world population at that time to be three billion persons. This would result in 30 billion fingers. For good measure he added toe prints—another 30 billion patterns. This brought the total finger and toe patterns to an estimated 60 billion prints. Maybe for ease in computations, he threw in another 40 billion to round off at 100 billion prints. How many points then would be needed to give odds of one in 100 billion of a duplicate pattern?

Going back to the survey for a moment, remember that the two “common” points repeat about one in ten times. Therefore, the chance that one of these points would duplicate would be 1/10 (one in ten). Now, of one point has a 1/10 possibility of duplicating in another pattern, two points would be the product of 1/10 times 1/10 for one chance in one hundred (1/100). For each additional point added the previous total would be multiplied by the same 1/10 factor.

To establish odds of a print duplicating once in 100 billion times, the 1/10 factor would have to be multiplied together 11 times. Thus using this line of reasoning, 11 points in a print could be said to have a possibility of duplicating only once in every 100 billion prints.

To sum it up, according to this survey, if 11 of the “common” points (ridge endings or bifurcations) were in agreement, the chance of duplication would be one in 100 billion, or more than 30 times greater than the world population.

Variations of the Minimum
Expanding on this formula, Mr. Gupta cuts the minimum points required from 11 to nine if pattern type, core, delta, ridge count, etc are visible. Also, for each “uncommon” point found, the total could be reduced by one. For example, a partial print does not show general characteristics. It does show seven of the “common” ridge endings or bifurcations, and two “uncommon” points, for a total of nine characteristics. To this total of nine add two because of the two “uncommon” points and the resulting “score” is 11.

Another example is a partial print showing general characteristics, such as pattern type, core, delta and ridge count. It also shows seven points, five of which are the “common” designation, and two of the “uncommon” type. To these seven points add two because the general characteristics are present, and two more for the two “uncommon” points and the resulting “score” is again 11.

The identifications in both of these examples would be equally as positive as a print containing 11 “common” points but lacking general characteristics.

Additional Study Needed
As in Santamaria’s study, an arbitrary value has been given to various characteristics. In the case of this study, the value is either one for “common” points or two for “uncommon” points. Yet the author’s survey shows that some points occur only once in 200 patterns. These are rated at two, along with other “uncommon” points. Another point in this group averages seven occurrences in 200 prints. It should be noted, however, that Mr. Gupta points out that this is only a preliminary study and as such can only show a trend that indicates some formations deserve more weight than others. He stresses the necessity for additional studies to fix qualitative values for ridge characteristics. These values could then be combined with the quantitative approach in use today.

Your columnist queried Director J. Edgar Hoover as to any study the FBI may have conducted along similar lines. Mr. Hoover’s reply, in part, was, “We have not conceived any system for qualitative analysis of ridge characteristics inasmuch as efforts along this line have not been sufficiently convincing…nor have we maintained statistics on the comparative frequency of certain ridge characteristics as opposed to others.”

(Grammar and spelling corrections made by Charles J. Parker, 10-13-2007)

(Originally printed in Finger Print and Identification Magazine, Vol. 52 No.11 ; May 1971)


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