One of the largest and best friction ridge look-alikes ever recorded, e.g., one of the largest and best amounts of corresponding ridge features ever seen in a non-match, was presented during latent print examiner training at the Chesapeake International Association for Identification Educational Conference in 2007 (see below).

Inked Print                                                         Latent Print

A cluster of 15 look-alike ridge features, bearing various levels of clarity, ridge reliability and quality of agreement, were found during a sexual assault investigation in the District of Columbia and was revealed following an IAFIS search of the FBI criminal database conservatively estimated to contain 53 million individual ten-print records (see below).
 

                          Inked Print                                                     Latent Print 

15 “corresponding” ridge formations in an inked print and latent print from different individuals were marked in red during the presentation (click on the image to view the corresponding ridge formations marked in red more closely).

 
                                                                 


                         Inked Print                                                       Latent Print

5 non-corresponding ridge formations are marked in green in the latent print and 10 non-corresponding ridge formations are marked in green in the inked print.

The T-Model Tested Against the Chesapeake IAFIS Look-alike

The T-Model was used to estimate the number of look-alikes and subsequently test its ability to correctly identify one of the largest and best friction ridge look-alikes as insufficient to infer positive identification.

The T Model was applied only to the amounts of “corresponding” ridge formations observed in the latent v. exemplar print impressions found in the Chesapeake IAFIS Non-Match.  Based on conservative interpretation of quantitative weights and conservative assessment of quality of agreement, e.g., applying lower bound quantitative weights and qualitative metrics to pairs of corresponding ridge features (see below quantitative and qualitative numeric scales), the estimated number of look-alikes calculated for the aggregate amount of corresponding ridge formations observed in the two impressions was calculated.

Click here to view PDF versions of the below qualitative scales and quantitative weights used to assess the Cheasapeake IAFIS Non-Match.

A Summary Quantitative-Qualitative Analysis of the Chesapeake IAFIS Look-alike

A summary quantitative-qualitative analysis, comparison and evaluation of this IAFIS non-match is presented.  Although effort was made to apply objective observation and conservative interpretation and assessment of ridge formation types and their agreement, and apply lower bound values for any ambiguity, final quantitative weights are based on measurements and professional judgment and cannot be precise.  The nature of measurement is relative, which makes precise measurement and agreement unrealistic.

Summary Analysis, Comparison and Evaluation the Chesapeake IAFIS Non-Match

The amounts in the inked and latent prints were examined at approximately 25x magnification.  Each of the ridges in the two impressions were run and ridge units were examined and compared one after the other throughout the pair of fingerprint impressions.  No pores or pairs of continuous ridge units between the two impressions with ridge widths and edge contours in agreement were found.  There were no pairs of scars or creases found in agreement between the two impressions with exception of the marked ridge formations.  The amount of “corresponding” ridge formations in the two impressions were located inside a diminishing area funnel pattern in which the number of ridges at the top of the funnel was over twice the number of ridges at the apex.  Distal measurements of the corresponding funnels were found to be within friction ridge skin elasticity threshold tolerances.  As a result, each pair of “corresponding” ridge formations in the two impressions was subject to reduction based on the presence of pattern force.  The quality of the ridge formation types in both latent and exemplar impressions as well as their quality of agreement were each assessed using conservative, lower bound values.

Click here for PDF summary analysis of Chesapeake IAFIS Latent.

Click here for PDF summary of analysis of Chesapeake IAFIS Exemplar.

Click here for PDF summary of comparison of Chesapeake IAFIS latent v. exemplar.

The total value, e.g., T-Value (T), for the Chesapeake IAFIS Non-Match is estimated by multiplying the values for the comparison of the latent v exemplar (see above PDF summaries) as follows:

(5) x (10) x (1) x (2.5) x (1.875) x (10 x (10) x (10) x (10) x (10) x (7.5) x (1.25) x (1) x (5) x (1) = 1,098,632,812

Based on a fingerprint population (R) of 530 million (e.g., the rough size of the FBI IAFIS database at the time of the search), the total value for the amount of corresponding ridge formations in two impressions, e.g., 1,098,632,812, the number of look-alikes (L) present is estimated as follows: 

Based on T-Model formula, the number of parts (P) is estimated as follows:

T^P = F

(1,098,632,812) ^ (P) = 10^120

Log (1,098,632,812) ^ (P) = Log 10^120

(P) (Log 1,098,632,812) = Log 10^120

P (9.04) =120

P = 13.27

The subsequent number look-alikes estimated is calculated as follows:

L = (R) (P) / T
L = (530,000,000) (13.27) / 1,098,632,812 = 6.4

The T-Model estimates the number of close matches or look-alikes for the amount of corresponding ridge formations in the FBI IAFIS database to be roughly 6.4.  As a result, the  amount of corresponding ridge features present in the two impressions is insufficient to infer identification. 

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The Chesapeake IAFIS look-alike represents one of the largest and best amounts of corresponding quantitative-qualitative ridge features that the author has ever seen in a non-match. 

Latent print examiners may use the T-Model Fingerprint Calculator to test and experiment with different arrangements of corresponding ridge features found in any latent v. exemplar fingerprint impressions.