Fingermarks are left on a surface because we are constantly secreting water and body oils and other compounds through our pores. This material is left on the surface we touch in the form of a mark. Fingermark evidence is very fragile-a touch would destroy one and must be collected and analysed with care, there are 5 different methods that can be used to collect latent fingermarks. We will explore some of these techniques in this investigation. The first is dusting, this method is best used on non-porous surfaces, it involves powder being sprinkled over the place where the fingermark is suspected to be, the powder will stick to the sweat and oil, and the fingerprint is revealed. The excess dust is then brushed off before the fingerprint is either photographed or lifted using sellotape. For porous surfaces, iodine fuming may be used; this method produces a yellow-brown non-permanent print, which must be photographed, by exposing the material to iodine vapour, which reacts to the sebum. The ninhyndrin spray can be used to reveal fingerprints on objects like books or paper that are over 30 years old. Silver nitrate can be sprayed onto a surface, or applied with a brush or swab, then if allowed to dry and put under ultra violet light, the fingerprint is revealed. It will need to be photographed, as the print will disappear after a short time. The last method of revealing fingerprints is superglue fuming, the superglue vapour reacts with the water in a print, the object with the print will have to be placed in a sealed tank to do carry out this method, as the fumes are dangerous to humans. This method will show the fingerprints in a greyish tone. Once fingerprints have been collected they will be compared with the suspect. Fingermarks can be developed on objects that have been in water. Furthermore, marks can be developed off skin (such as from the neck of a strangulation victim). Items found in water, snow, or mud may also yield prints, but before you any attempt to process it or pack it for shipment to the crime lab, it must be allowed to air dry. For latent prints, the biggest problem is to make them visible. However, if left untouched, they are virtually permanent – latent prints have been found in ancient Egyptian tombs! There are very few surfaces on which a print cannot be developed.
Fingerprint matching was traditionally done manually, but this has been revolutionised by computer technology. The Avon and Somerset Police Force was a pilot for the National Automated Fingerprint Identification System (NAFIS), which was introduced in 1996, the system has since been rolled out nationally. Scanners now record each unique feature of a fingermark and store the data on a computer. The system means that we can use even a tiny scrap of a fingermark to search a national database holding the impressions of more than 5.5 million people.
Method
Part 1- Several fingermarks were made on a white tile and then developed by lightly dusting the tile with Aluminium powder using a squirrel hairbrush. This method is often showed being used by detectives in movies. Minute particles of powder cling to the print residue as the brush passes over. Care was taken not to brush over the marks too heavily as this would distort the detail needed for comparison. Then, a small piece of sellotape was placed over the clearest fingermark to lift the mark, ensuring that any air bubbles were removed using a roller. The tape was then carefully peeled away from the tile and then placed onto a clear piece of plastic in order to preserve the detail. This procedure was repeated several times until good prints had been collected.
Part 2 – A fingermark was made onto a piece of black plastic by squeezing it with the thumb and the index finger. It was then secured to a lid and placed inside a flask, which contained water and a small metal plate, which contained superglue on the surface of the water. The flask was then left in a heater for around 5-10 minutes. Superglue vapour reacts with water in the mark (bonds in seconds) will coalesce inside the print residue to reveal a latent print. The flask was then removed from the heater and the black plastic, was removed demonstrating a clear white fingermark. Placing it on a piece of clear plastic and covering it with some sellotape then preserved the print.
Part 3 – Prints were made of each finger and each thumb on both hands by gently rolling them in an inkpad and then rolling from left to right onto an elimination sheet in the appropriate box.
Part 4 – At this stage a magnifying glass was used to detail the ridge patterns in the fingermark and visually compared using the elimination sheet of the sample fingerprint impression (R. Middle Finger) for configuration, sequence and relationship. The patterns of similarity identified were recorded (numbered) in a clockwise direction, starting from the top right on the plastic covering the fingermark. The points of similarity were also recorded on the elimination sheet.
Discussion
The results of part one of the investigation were very good. The fingermarks lifted were very clear this enabled the identification of several details (Galton). It was clear early on in the investigation how easy it was to destroy the fingermark as the smearing or retouching of a mark was easily done, this ruled out these marks for be use in the comparison process (part four), in which a very clear mark was required. The lifting of the mark proved slightly difficult as air bubbles in the sellotape interfered with the whole mark being recovered. Once the bubbles were removed using a roller and the tape lifted, it was a straightforward process. By placing the prints on a piece of clear plastic in front of a dark background, they were viewed more clearly and would help in the identification of detail. I found that lightly powdering over the mark helps to improve the visualisation, as for the first few attempts; the details were distorted due to excess powder and too much force. It was also difficult not to distort the fingermarks by getting marks on the sellotape and greater care was required.
The results for the second part of the investigation proved slightly harder to obtain. It was necessary to repeat the exercise twice, as in the first attempt, not enough superglue was used on the dish, so not enough vapour was absorbed to produce a good visible mark. When repeated with slightly more superglue, the print obtained was much clearer. However, after being preserved for several weeks, the mark appears to have disappeared on both sides (see Fig. 4). It is possible that the visual mark might have been disintegrated as a result of oxygen coming into contact with the surface. It is therefore suggested, that to maintain the image of the mark it would have been better to take a photograph, something I have failed to do.
The elimination prints came up reasonably well, although there are several prints with the edges missing (see Fig.5). This is due to the fact that when one rolls their own finger, the pressure is on the bottom of the finger and it is quite awkward to press down at the top. This is illustrated by the fact that the rolled fingerprint edges are missing, whereas the plain impressions, where the other hand was used to place pressure over the whole finger, were perfectly formed. The quality of the rolled prints could have been improved by having a second person roll the finger, as a police officer would do in this situation at the station, as they would place even pressure over the whole finger and thus produce a complete print.
As a result of good marks being obtained using the dusting method (part one), it made the comparison in part four easier. However, due to the fact that the mark using the superglue fuming was not visible, it resulted in not being able to use these in the comparison process. Some of the details on part of the prints were missing in the elimination process and as a result any match that may have been made in this area could not be. However, several details were identified: first of all the size of the print, the direction of the loop (gave an indication of which hand it came from) and also 7 detail matches (as shown on Fig. 3 & 5). It would have been possible to improve the details found by simply producing better elimination prints. However, one should remember the in an actual fingermark evidence case, it is unlikely to gain a very high quality print, therefore the results demonstrate more realism.
No two-fingermark impressions from the same finger are identical due to several factors. First of all, pressure makes a big difference to the mark. If a lot of pressure is applied to one and not the other, there will be a big difference in clarity, size and spacing between each detail. Also, as shown in the results of the elimination prints, if pressure is only placed on one area of the finger, the print will be missing various details from the area not under pressure. Secondly, the surface on which the mark is made will have an effect. If the surface is uneven or rough, the same mark will appear very differently on a smooth surface. Also, the angle of impact will have an effect in the same way as pressure, as some details may not show. The details themselves will never change, but several factors can affect the mark produced. Finally, I found in the practical, that some of the fingermarks left on the tile (in part one) were more visible than others, this may be due to a reduced amount of secretion of water and body oils and other compounds through our pores at the time of impression, thus reducing the level of visible detail. As a result, no two fingermarks from the same finger are identical.
As stated earlier, it is not necessarily important to find 16 points of agreement in order to identify a mark as having come from a particular finger, as there maybe other factors that can be taken into consideration. In many fingermark evidence cases, the actual mark left at the scene will often be of a partial mark of the finger. In such cases for example, where the suspect’s mark is only partial and only some details can be found, but a scar is found in exactly the same place on the same finger, same size and same shape as the fingerprint of the suspect, it would seem reasonably conclusive it came from that person.
The method of using Aluminium powder to visualise the fingermark was very effective on a smooth surface. The marks lifted were very clear and could easily be used as evidence. The method of using superglue to visualise the mark was effective at the time, but the preservation of the mark proved somewhat of a problem, this could have been maintained by taking a photograph. The elimination prints came out reasonably well and could be improved if someone other than myself were able to hold my fingers down in the correct angle.
Fingerprinting is a skill and it takes a lot of time and effort to clearly identify a person from a set of marks. The laboratory conditions enabled the ability to obtain good marks and prints; this is compared to a crime scene, in which points in agreement are more difficult to find.
Although fingerprint evidence remains one of the main types of evidence for identifying a suspects guilt or innocence, and the results of the investigation proving conclusive. Fingerprint comparison is not an exact science. Indeed if it was then identification would be a matter of statistical analysis and we wouldn’t need the skills of the experts at all. Identification by fingerprint whether based on 8, 12, 16 or 24 points is a matter of opinion not fact. It has always been open to the defence to challenge fingerprint evidence, even where it apparently meets the national standard.
Whilst the ‘numeric’ standard continues to be applied across the UK, and some European Countries, others, notably, in North America, apply non-numeric standards, based on more principles, which determine the quality and sufficiency of the ‘ridge detail’ rather than numeric sufficiency. It would seem this system would have a greater scientific value.
Fingerprint Whorld, Vol 22 No 84 P78
