Advanced Latent Fingerprint Techniques for Detection and Analysis on Documents

Introudction

Fingerprints are characteristic ridge patterns that are present on all the fingers of every individual. These ridge patterns, along with the secretions from the skin surface, form fingerprints. These patterns remain constant throughout the life of an individual and differ from those of another person. The fingerprints vary not only from person to person but also among various fingers of each hand. Therefore, fingerprints form an essential characteristic of individualisation. This is because fingerprints are unique patterns that do not change throughout the lifetime of an individual. Identical twins might have the same DNA, but they have different fingerprints. 

Very often, the criminals leave their fingerprints at the scene of the crime knowingly or unknowingly. Based on the type of print left at the scene of the crime, fingerprints are divided into three types:

1. Latent,
2. Patent, and,
3. Plastic prints.

Patent fingerprints are those that are visible to the naked eye, whereas latent fingerprints are invisible to the naked eye, and plastic prints are those that have a three-dimensional impression. The fingerprints found at the crime scene can be either of these. However, since criminals try to protect themselves from getting caught, they end up leaving latent prints at the crime scene. The forensic scientists who visit the crime scene for evidence collection have to be very diligent and careful, as the latent prints need to be detected and developed.

The detection of latent prints is a tough job as their exact location is difficult to trace. Once detected, the fingerprint analysis can be done, and the culprit can be identified.

How To Become a Fingerprint Examiner?

Link between the Latent Fingerprint and Questioned Documents

Whenever a person tries to deliberately tamper with a document by alteration or obliteration, they might leave their latent prints on those documents. If a document is suspected of having latent fingerprints on it and the authenticity of the document is also in question, first, the questioned document is sent for fingerprint detection and collection. This is due to the fact that the necessary document examination might lead to tampering of evidence and loss of potential clues. One important factor that must be kept in mind while developing the latent fingerprint is that the methods of development might affect the evidence of a questioned document. For example, if chemical methods are used for development, the chemicals might interact with the inks present in the document.

Different scenarios of fingerprints on documents might be observed in cases related to check fraud, insurance fraud, forged signatures and so on. Another way in which the latent prints might get transferred from the culprit to the document is when he tries to misplace it or change its location. This type of case arises when the culprit is trying to hide a document so that it cannot be found or tries to exchange an authentic document with a mere copy. Even when a person tries to set a particular document on fire, suppose when he tries to completely remove its existence, in half-burnt or edge-burnt documents, the fingerprints can be present. Often, death threats are given to people in written form, which might contain the fingerprints of the person doing so. If analysed carefully, the path to the culprit can be traced back.

The principle behind the presence of latent print on the document is based on the interaction between the ridges of the finger and the porous surface of the paper. To solve a Criminal Investigation, the detection analysis of latent fingerprints is of utmost importance. However, the questioned document suspected of having latent fingerprints should be handled with great care lest the fingerprints might get damaged owing to their invisibility. Some traditional methods were initially employed for this purpose, but with the advancement in studies and science, new methods have been developed for detection and analysis purposes, which will be discussed in this article.

Some significant points to detect forgery in Documents using Latent Fingerprint

1. Authentication – fingerprints are used many times to authenticate a document. This provides an extra level of protection and prevents the document from being forged.
2. Inability to be forged – even though the criminals can necessarily forge the documents by changing their meaning or making minute alterations and obliterations, the fingerprints present in the latent format cannot be easily altered by the criminals.
3. Less chance of removal – even if the criminal succeeds in tampering with the document, making its authenticity and integrity questionable, they fail to remove fingerprint traces from the document if the prints left are latent and invisible to their eyes.
4. The possibility of generating a genetic profile – fingerprints are formed on a surface only after it is touched. This contact causes touch DNA to be left at the scene of the crime. From the touch DNA, the genetic profile can be generated using various advanced techniques. Even though the low quantity of DNA can be a concern, research has been conducted to overcome it.
5. The Automated Fingerprint Identification System (AFIS) – AFIS provides an important computer database for the comparison of fingerprints. It operates as a biometric tool for maintaining a record and reference list, which is widely used in forensic science to establish identity whenever an unknown fingerprint is encountered by the forensic document examiners.

Advanced Technique For Latent Fingerprint Detection On Questioned Documents

The presence and proper detection of latent fingerprints at the crime scene are significant because if the prints are not properly detected and developed in the first place, it might lead to the loss of important evidence. Earlier, some simple methods of detection based on biochemical reaction and physical absorption were employed in the case of latent fingerprints on porous surfaces like paper. These include the ninhydrin method, the cyanoacrylate fuming, the powder dusting method and the silver nitrate method. These methods, though easy, had a few disadvantages like destructiveness, the requirement of pre-treatment and possible health hazards. Nowadays, advanced techniques of fingerprint detection have been employed to try to overcome most of the disadvantages of the old techniques.

1. Ultraviolet Laser-induced fluorescence detection technology – in this method, the document is exposed to ultraviolet laser light. The constituent of the latent fingerprints, which are present in trace amounts, shows fluorescence when ultraviolet laser light is incident on it. Photodetectors are used to collect the emitted fluorescence. This technique provides high-resolution, non-destructive, and no-contact detection methods. Using this method, the image of a latent fingerprint can be formed immediately, and more than ten secondary features of a fingerprint can be detected, which provides enough clues for individualisation.
2. 1,8-Diazafluoren-9-one (DFO) Method – this method has replaced the use of ninhydrin to detect latent fingerprints. In this, the document containing latent fingerprints is allowed to react with DFO. The amino acid residue of the fingerprint reacts with DFO to form a pink or faint red coloured product which shows intense fluorescence under green light. Unlike the ninhydrin method, this requires high-temperature and low-humidity conditions. There is also no need for post-treatment of the product for fluorescence. The number of latent fingerprints developed by this method is higher than that with ninhydrin.
3. Use of quantum dots in powder dust method – quantum dots present in the powder adhere to the oily or aqueous substances present in latent fingerprint based on adsorption and attraction based on electrostatic forces. The quantum dots adhering to the fingerprint are exposed to oxidation and therefore develop a low contrast, which in turn causes long-term preservation of the developed fingerprints. To prevent the oxidation of quantum dots, they are coated with some material.
4. Use of quantum dots in liquid – in the liquid development method, the quantum dots chemically react to specific substances present in the fingerprint. Often, this method is modified by using typical ligands and functional groups. After the chemical reaction, if the product is exposed to 440nm blue light or 365nm UV light, it will develop the required contrast.
5. Use of rare earth upconversion fluorescent nanomaterials – this process makes use of rare earth-doped material, which gets excited by longer wavelength light and emits light of shorter wavelength. The background fluorescent interferences can be avoided as these materials get excited by NIR light. These substances, when used for the development of latent fingerprints, give much better results than the traditional powder methods. This method, when applied to Chinese paper money or note paper, shows autofluorescence, and the contrast developed shows no background interferences.

Advanced Techniques For The Analysis Of Latent Fingerprint

Once the latent fingerprints are detected on questioned documents, the process of their enhancement and analysis begins. The conventional steps followed in different forensic science labs include analysis, comparison, evaluation and verification.  Analysis of fingerprints is done by first identifying and extracting the ridge characteristics and fingerprint patterns, followed by their comparison with the standard reference of fingerprints. Once compared, the evaluation process begins where the forensic experts evaluate the results obtained from the previous step, followed by its verification. This, however, is a very lengthy procedure where inaccuracies might also be present. Here comes the use of an automated system of latent fingerprint analysis to make the process more efficient and accurate. In this method, fingerprints are basically analysed to identify an individual.

1. Use of convolutional neural networks (ConvNets) – here, an automated latent fingerprint recognition algorithm is used which makes use of (ConvNets) for the estimation of ridge flow, an extraction based on minutiae descriptor leading to the extraction of complementary templates which includes two minutiae and one texture templates for the representation of latent fingerprint. With the help of this method, the experts are able to create a short list of reference candidates from the available list of references, depending on the comparison score of latent fingerprints and references based on the complementary templates.
2. Use of generative adversarial networks (GAN) – this method uses a specific algorithm to enhance fingerprint characteristics after they have been developed. It focuses on improving the poor ridge characteristics so that the prediction of ridge information becomes possible. It has been observed that this method preserves the ridge characteristics and enhances the quality of fingerprints. Overall, this system improves the possibility of latent fingerprints matching by enhancing the characteristic features.

Conclude

Fingerprints are so unique that they can be used for individualisation. In case of questioned documents, several types of evidence can be found, one of them being latent fingerprints. The evil intention of the criminals leads to them depositing their latent fingerprints unconsciously on the document. Only with the careful observation of the examiner can he determine if there is a possibility of finding latent prints on any paper surface. The conventional analysis of fingerprints has its own pros and cons, which is why there is a need to keep up with the advancements in science. Therefore, advanced technologies have been employed to overcome the drawbacks of the old methods. The recent techniques are better in terms of sensitivity, specificity and efficiency. More such advancements are expected to take place in the future, which might be enough to completely replace conventional methods.   

References

1. Bumbrah GS, Sharma RM, Jasuja OP. Emerging latent fingerprint technologies: a review. Research and Reports in Forensic Medical Science. 2016; 6:39-50
   https://doi.org/10.2147/RRFMS.S94192
2. Liqing Ling, Lihua Huang, Kai Guo, Huijie Huang, “Detection of latent fingerprints on papers,” Proc. SPIE 11170, 14th National Conference on Laser Technology and Optoelectronics (LTO 2019), 111703B (17 May 2019); https://doi.org/10.1117/12.2533904
3. Wang, Meng, Ming Li, Aoyang Yu, Ye Zhu, Mingying Yang, and Chuanbin Mao. “Fluorescent nanomaterials for the development of latent fingerprints in forensic sciences.” Advanced functional materials 27, no. 14 (2017): 1606243.
4. Prabakaran, Eswaran, and Kriveshini Pillay. “Nanomaterials for latent fingerprint detection: a review.” Journal of materials research and technology 12 (2021): 1856-1885.
5. Ling, Liqing & Huang, Lihua & Guo, Kai & Huang, Huijie. (2020). Detection of fingerprints on porous papers and performance evaluation. Optics Communications. 475. 126276. 10.1016/j.optcom.2020.126276.
6. K. Cao and A. K. Jain, “Automated Latent Fingerprint Recognition,” in IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 41, no. 4, pp. 788-800, 1 April 2019, doi: 10.1109/TPAMI.2018.2818162.
7. https://hawkeyeforensic.com/2024/05/09/fingerprints-as-forensic-evidence-in-document-authentication/

Author Bio

Read More Articles