Evaluating the Degradation Relationship Between Latent Print Impressions and Touch DNA Under Varying Environmental Conditions

Latent prints have been processed as a source of touch DNA evidence in the hopes of attaining partial or even full DNA profiles. However, the relationship between the latent quality and the DNA quality has not yet been fully explored, resulting in gaps in understanding how the two are connected. A common source of touch DNA is from latent print evidence, which is typically processed and photographed at a scene, and subsequently processed for DNA in the laboratory. However, there is skepticism in the forensic community around touch DNA as laboratory procedures are often manipulated beyond standard operating procedures to produce a better yield and profile. Both latent print and touch DNA analysis can provide valuable information that can assist in connecting the evidence back to the print’s contributor and the known DNA profile. Presently, there are issues regarding the current knowledge of what variables influence the deposition, transfer, and persistence of touch DNA as well as how touch DNA can be interpreted in relation to the event(s), especially when contrasted with perception around more traditional DNA sources. The purpose of this study was to provide insight into the degradation of latent prints and of touch DNA as well as any relationship between the two, under different combinations of environmental factors. Latent prints deposited on glass slides were exposed to environments controlled for varying degrees of lighting, temperature, and airflow, for periods ranging from 1 week to 4 months. Both the latent prints and their respective touch DNA samples were evaluated with both qualitative and quantitative measurements to assess degradation in each condition. Once the degradation of both the latent prints and the touch DNA were evaluated individually both qualitatively and quantitatively, the relationship of degradation between the two were assessed in each condition set. The presence or absence of degradation relationships in common environmental conditions can supply insight into crime scene reconstruction as well as guide the approach taken by crime scene investigators in evidence collection and processing techniques to maximize the collection of pertinent evidence. With these findings, crime scene investigators will be able to have a better idea of the value of latent print evidence at a scene based on the exposure to, or lack thereof, different environmental influences. Additionally, the data may aid in more accurate interpretations of the circumstances a piece of evidence (latent/touch DNA) may have been exposed to prior to collection and processing. Currently, there is a general understanding of the influences that play a role in the degradation of both latent prints and touch DNA, however with a more in-depth comprehension of these influences and the degradation relationships between the two, the more accuracy and precision examiners can bring to evidential interpretation. Overall, this research aimed to supply practitioners with the ability to take these known and extensively studied influences on the relationship between a latent impression and its touch DNA into consideration when assessing casework and furthermore, creating an improved rendering of the scenario with those results