Friction Ridge Identification involves the use of friction ridge impressions - whether they are patent or latent, clear or unclear; 'large' or 'small' (all prints are partial) that are found at crime scenes in order to help solve the crime.
First, the impression is found and collected at the crime scene by a highly trained individual in the collection of crime scene evidence. It is brought to the friction ridge identification specialist (sworn officer or individual who is not sworn) who analyzes it and then compares it to a known fingerprint. Based on the information gathered during the analysis and, the information obtained through the comparison of the unknown print to the known print, an evaluation as to its source of origin, is completed. In other words, the goal of individualization is attained or not attained. There is only one source from which the crime scene print originated.
The analysis phase involves collecting information about the crime scene print. Questions such as the following are hopefully answered: Where was it found? What was used to enhance the print? (eg. black powder, white powder, ninhydrin or perhaps the impression was made in dust and photographed) How has the surface from which the print was lifted affected the appearance of the lift? How has the enhancement process affected the appearance of the friction ridges? What type of distortion is present? (many different kinds may be apparent on one lift) How does the clarity or lack of clarity affect the amount of detail that is present in the unknown print? Also, how does the clarity or lack of clarity affect the level of tolerance for any ridge formation discrepancies between the unknown and the known print in the comparison phase? Do you have sufficient quality and quantity of information to proceed to the comparison step in the identification process? (It's important to note here that quite often certain information, such as types of distortion present, are not always obvious in the friction ridge impression at this stage and may be revealed later on in the comparison stage.)
The comparison of the unknown to the known is a very objective process. Others must see what the identification specialist sees.
Next, the evaluation is made based on the identification philosophy. The identification philosophy can be paraphrased by the following statement:
"Friction ridge identification is established through the agreement of friction ridge formations, in sequence, having sufficient uniqueness to establish individuality." David Ashbaugh 1999
Not everyone, however, agrees with the term 'sufficient uniqueness' and therefore you might want to consider paraphrasing the identification philosophy as follows:
Friction ridge identification is established through the agreement of friction ridge formations, in sequence, having sufficient 'observed' uniqueness to establish individuality.
As previously mentioned, before the friction ridge identification specialist can answer questions, however, such as "Is there agreement of friction ridge formations?" "Is there sufficient 'observed' uniqueness to establish individuality?", it is imperative that he/she must first understand the premises of friction skin identification and how scientific research in biology, histology, embryology etc. has supported these premises...primarily the uniqueness and permanency of friction skin.
"As long as the examiner has a firm understanding of uniqueness origins which develop friction ridge structure cell by cell, the eye can be trained to distinguish all its manifestations." David Grieve
Last, but certainly not the least, is the process of verification to be completed by a second qualified friction ridge identification specialist. This step is not to be treated lightly and is extremely important in order to follow the criteria that contributes to making fingerprint identification a 'science'. Verification ensures the application of a proper sequence of events has been implemented by the identification specialist in arriving at making a positive identification (and sometimes non-identification). Verification also ensures objectivity in the comparison of the unknown print to the known.
This scientific process of analysis, comparison, evaluation and verification (A.C.E.-V.) is known as the identification methodology or, "a structured and systematic manner in which quantitative-qualitative analysis of friction ridges is carried out". (Quantitative-Qualitative Friction Ridge Analysis, Introduction to Basic Ridgeology by David Ashbaugh May 1999, pg.75).
This document provides a comprehensive look at the 'Friction Ridge Identification Process' using a 'five-step' scientific methodology - another way of interpreting A.C.E.-V.
Pat Wertheim's answer of "reliable predictability" as to 'when' the friction ridge identification specialist actually makes a positive identification is explored.
Therefore another way of interpreting the Identification Philosophy could be:
The biological uniqueness and permanence of friction ridges allows for identification or 'individualization' of a friction ridge impression. Identification is established when there is sufficient quality and quantity of information present in both the unknown print and known inked print such that each isolated friction ridge formation or feature selected in the unknown print can be readily located and found to be sequentially in agreement with the inked print. In other words, identification is established at the moment in time when there is 'reliable predictability'.