Abstract
DNA persistence and DNA transfer are important features in the assessment of a crime scene. The question how long DNA may persist at a certain location is similarly important as the one how the DNA has been transferred to this location. Depending on the source of the DNA as well as the conditions at the crime scene, the answer to this question is quite difficult. In this study, persistence of DNA from epithelial abrasions, blood cells, and saliva cells in indoor and outdoor scenarios has been investigated with regard to exposure time and exposure conditions including sunlight, temperature, and humidity in summer and winter scenarios. Overall, we generated 338 epithelial samples, 572 blood samples, and 572 saliva samples. A complete profile of the cell/DNA donor after exposure could be obtained in 47%, 65%, and 58% of epithelial abrasions, blood samples, and saliva samples, respectively. Regarding blood samples, there were no differences between supporting materials cloth and plastic; however, the percentage of complete profiles was higher for saliva samples on plastic and for epithelial samples on cloth. In indoor scenarios, complete profiles could be recovered from nearly all blood and saliva samples up to 9 months, whereas the amount of epithelial complete profiles already started to decline after 3 months. In outdoor scenarios, we observed a tipping point at an exposure time of 3 months. Blood and saliva samples collected after this period displayed complete profiles in less than 25% of samples. After 12 months, no outdoor sample showed a complete profile. The results of this study facilitate decisions on the relevance of recovered DNA from crime scenes.
Highlights
The great progress in forensic DNA analysis has led to DNA testing being conducted regularly and on a large scale during police investigations [1], since it is possible to create DNA profiles from even the smallest amounts of DNA secured at a crime scene [2]
Similar values could be obtained in outdoor scenarios with a mean loss of 92% and 97%, with a greater range (0–47% and 0–9% recovery rate for blood and saliva, respectively)
DNA amount after 1 month varied between 1.7 ng and 25.3 ng in the indoor scenarios, whereas 0–11.5 ng DNA could be found in epithelial abrasions regarding outdoor scenarios
Summary
The great progress in forensic DNA analysis has led to DNA testing being conducted regularly and on a large scale during police investigations [1], since it is possible to create DNA profiles from even the smallest amounts of DNA secured at a crime scene [2]. Depending on the source of the DNA as well as the conditions at the crime scene, the answer to the second question is quite difficult. While several studies deal with the possibilities of DNA transfer [e.g., 6–9], studies on the persistence of DNA are still rare and have mostly been conducted under laboratory conditions [10–13]. Investigations of outdoor scenarios are mainly limited to restricted conditions [14–19]. A recent study run in Singapore under tropical conditions showed that DNA persistence on items left outdoors showed a great variation, mostly dependent on the amount of rain [20]. We investigated DNA samples from epithelial abrasions, blood cells, and saliva cells in indoor and outdoor scenarios under humid temperate climate conditions
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