DNA recovery from latent fingermarks treated with an infrared fluorescent fingerprint powder

Quantifying DNA loss in laboratory-created latent prints due to fingerprint processing

Fingerprints, which are associated with touch samples, typically contain a limited amount of DNA. The amount of available DNA can be further reduced when the same touch samples undergo fingerprint processing [1]. The fingerprint development process consists of high-powered lighting (inherent luminescence and UV light) and chemical compounds (ninhydrin, black powder, cyanoacrylate, and rhodamine 6 G) which could reduce DNA quality and quantity. Therefore, forensic scientists often must select one type of analysis over the other due to the destructive nature of processing. DNA and latent fingerprinting are both useful sources for identification, although both can produce partial results. A partial DNA profile may only contain a few alleles, limiting the ability to identify a potential suspect to perform comparisons. A partial fingerprint generally means that only a very small part of the fingerprint is present, which makes comparisons difficult. Because partial results are common, combining data from both fingerprinting and DNA analysis would increase the confidence of an identification of a person. Significant research has been performed to determine if a DNA profile can be obtained from latent processed fingerprints; however, there has yet to be research done in a standardized manner. In this study, we used standardized mock "fingerprints" in order to reduce fingerprint DNA variability and specifically focused on DNA quantitation after each step in the fingerprinting process. Results suggest that latent print processing techniques used on non-porous surfaces (plastic, duct-tape, metal, and rubber) do not affect DNA quantity or quality. In contrast, ninhydrin, a chemical used for processing fingerprints present on porous surfaces (wood and paper), significantly reduced DNA recovery. Together these results suggest that DNA can still be performed on latent print processed items, unless ninhydrin has been used.

Touch DNA Sampling Methods: Efficacy Evaluation and Systematic Review

Collection and interpretation of "touch DNA" from crime scenes represent crucial steps during criminal investigations, with clear consequences in courtrooms. Although the main aspects of this type of evidence have been extensively studied, some controversial issues remain. For instance, there is no conclusive evidence indicating which sampling method results in the highest rate of biological material recovery. Thus, this study aimed to describe the actual considerations on touch DNA and to compare three different sampling procedures, which were "single-swab", "double-swab", and "other methods" (i.e., cutting out, adhesive tape, FTA® paper scraping), based on the experimental results published in the recent literature. The data analysis performed shows the higher efficiency of the single-swab method in DNA recovery in a wide variety of experimental settings. On the contrary, the double-swab technique and other methods do not seem to improve recovery rates. Despite the apparent discrepancy with previous research, these results underline certain limitations inherent to the sampling procedures investigated. The application of this information to forensic investigations and laboratories could improve operative standard procedures and enhance this almost fundamental investigative tool's probative value.

Interpol review of fingermarks and other body impressions 2016-2019

This review paper covers the forensic-relevant literature in fingerprint and bodily impression sciences from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20 Review%20 Papers%202019. pdf.

A subsequent procedure for further deciphering weapons after application of the Trace Metal Detection Test (TMDT): Proof of concept

The trace metal detection test (TMDT) is an effective and convenient technique to potentially link perpetrators and metallic weapons by comparing morphological information of developed imprints and suspected weapons. However, metallic items without characteristic patterns and incomplete contact with weapons often lead to inadequate morphological features in developed imprints on hands, resulting in difficulty in identifying suspected weapons and a failure to demonstrate potential relationships between perpetrators and weapons. This paper presents a subsequent procedure, after application of the TMDT, for inferring possible weapon-source of a specific imprint. As a proof of concept, all the experiments involved metallic items as an example and were carried out under controlled laboratory conditions. An analytical method was established by selecting elements of interest in developed imprints from seven metallic items (three groups), undertaking quantitative ICP-MS determination of the elements, and comparing the elements in these imprints (inter- and intra-group comparisons) and with those in their source items. Using the established method, possible groups and types of source metallic items could be inferred based on elemental characteristics in imprints, under the premise that no other metal sources exist before or after contacting specified metallic items. This method could be useful for providing investigative clues and evidence of association for developed imprints that lack unique morphological features and for verifying the results of color reactions in the TMDT. For this reason, it can serve as a standard supplementary procedure after the application of the TMDT, which could further strengthen the correlations between perpetrators and weapons even common metallic objects.

Evaluation of DNA Extraction Methods for Processing Fingerprint Powder-Coated Forensic Evidence

In unison, fingerprinting and DNA analysis have played a pivotal role in forensic investigations. Fingerprint powders that are available on the market can come in a range of colors and with specific properties. This study evaluated the efficiency of DNA extraction from samples coated with 3 brands of fingerprint powders: Lightning, Sirchie, and SupraNano, covering a range of colors and properties. A total of 23 fingerprint powders were tested using the Chelex, Promega DNA IQ™, and Applied Biosystems™ PrepFiler™ DNA extraction protocols. The DNA IQ™ and PrepFiler™ methods extracted higher yields of DNA in comparison to Chelex, which also accounted for better quality of PowerPlex x00AE; 21 DNA profiles recovered. There were no signs of degradation or inhibition in the quantification data, indicating that samples returning low DNA yield was due to interference during DNA extraction and not PCR inhibition. DNA profiles were recovered from the majority of fingerprint powders with only a single powder, Sirchie Magnetic Silver, failing to produce a profile using any of the methods tested. A link was observed between the DNA extraction chemistry, fingerprint powder property, that is, nonmagnetic, magnetic and aqueous, and the brand of fingerprint powder. Overall, the DNA IQ™ method was favorable for nonmagnetic fingerprint powders, while magnetic fingerprint powders produced more DNA profiles when extracted with the PrepFiler™ chemistry. This study highlights the importance of screening DNA extraction chemistries for the type of fingerprint powder used, as there is not a single DNA extraction method that suits all fingerprint powder brands and properties.

DNA recovery from gelatin fingerprint lifters by direct proteolytic digestion

Fingerprints are a valuable source for DNA profiling in forensic investigations. In practice, the fingerprints are routinely visualized first by powder staining and then often transferred to tapes or gelatin lifters for storage or examination. If at all, fingerprints are usually sampled for DNA in a second step. To target the DNA sampling in an optimal way, it is essential to know how much of the DNA in the sample remains in place and how much is transferred to the lifter. In the present study we addressed this question analyzing 16 pairs of thumb prints and revealed that more than 80% of the DNA from a fingerprint is transferred to the gelatin lifter. Therefore, subsequent DNA sampling of the stored gelatin lifters appears more promising than recovery of the residual DNA from the original fingerprint. Furthermore, as a proof of principle, we developed a protocol for the direct extraction of DNA from gelatin fingerprint lifters by proteolytic digestion of the gelatin matrix followed by organic extraction. We show that DNA recovery from gelatin lifters by this direct extraction protocol is more efficient compared to swabbing the lifter followed by standard magnetic bead extraction of swabs. However, given the more elaborate protocol for direct extraction, we would still recommend the swab technique as the method of choice for forensic routine work.