2.4 The use of new technologies in fingerprint matching
The process of matching fingerprints found at crime scenes with reference fingerprints from potential suspects or others known to be present at the scene, is a highly skilled activity. Unambiguous and unchallengeable individualisations are most likely to result from complete, well-defined prints recovered from the crime scene. Problems are more likely to arise when a partial, smudged or otherwise distorted print is left at the scene, as was apparent in the Mayfield case where the initial US attribution of prints was erroneous.
The old UK system of requiring 16 matching characteristics to establish identity between a crime scene print and a file (reference) print has now been abandoned and there is no quantitative standard. Can you suggest one or two reasons why that may have happened?
One particular reason for the change is that a mechanical match of the previous kind does not answer the question of whether there are points of difference (discrepancies) between the prints as well as the matches. Another, related reason is that the formulaic match can give a false sense of certainty when there may in fact be some doubts as to the match. Another reason, which was seen in the McKie and Mayfield cases, is that once a potential match is found the examiner may feel that the job is done and that other possibilities need not be explored.
New methods of image enhancement are being developed. For example, the DCS-3 system is now part of IDENT1. The DCS-3 system comprises a high-resolution digital camera, various light sources and filters and complex software and it can be used to enhance fingerprints in a variety of ways to help the expert to examine the print in more detail. One example is shown in Figure 4 where a latent fingerprint on a vehicle is first visualised by fluorescent light (a) and photographed using DCS-3 (b) and that image is then digitally enhanced to give a final black and white image (c) which is best for detailed examination.
Although these image-enhancing methods are very useful, courts need to be reassured that the enhancement does not materially alter the features of the print. The DCS-3 system has built-in safeguards to ensure accuracy. In the electronic manipulation of the Madrid bombing fingerprint (Case Study 2) some of the detail was apparently lost or obscured, thus compromising the comparison. In all of forensic science the aim is minimum interference with samples left at crime scenes, as every new step introduces potential errors or changes.