Evaluation of collection protocols for the recovery of biological samples from crime scenes

Abstract

The main focus in forensic genetics in the past 30 years has been either to increase the efficiency of the extraction and identification of DNA from a wide variety of evidence, or to improve DNA profiling technology by making it more sensitive and robust. However, the methods used to recover DNA evidence from crime scenes have seen little development.
This research has developed wetting agents which can be incorporated into most conventional swabbing protocols and has the potential to significantly improve both the recovery rate and stability of the DNA bearing samples. The main objective of this research was to improve the efficacy of the processes of collection and storage up to the point where the evidential material is received at a laboratory. The effect of heat and time post-collection on degradation within collected samples before they reach the laboratory has been assessed.
Three collection methods of biological evidence have been compared: one swab, double swab and pipetting, using distilled water TE buffer and commercial cell lysis (Qiagen) as a wetting agent. An enhancement in quantity and quality of DNA was seen when the double swab collection method was used with the commercial lysis buffer. This led to the development of an in-house detergent based buffer to be used as a wetting agent. In addition, the stability of the DNA post-collection was greatly improved especially at higher temperatures, even with extended periods post-collection. When using ultrapure water as the wetting agent DNA degradation can be seen as early as 6 h at room temperature. However, the detergent-based solution stabilized DNA for up to 48 h, even when the temperature is increased to 50 °C. The impact of this study is likely to be limited in circumstances where crime scene evidence can be kept at temperatures below room temperature until it reaches the laboratory. However, in contexts where this is problematic, the modified method for collection could have a large impact on the preservation of forensic evidence before it reaches the laboratory.
The reliability of the results from analysis of evidential DNA is greatly improved when a careful protocol is observed for the collection, transfer and storage of the original samples. However, there is no published data on the development of protocols particularly suited to collection, transfer and pre-lab storage of samples, especially when there are extreme environmental conditions at the crime scene. The mechanisms of natural degradation of DNA are well understood (Hu et al., 2005) and temperature and moisture content pay a significant role. In the climatic conditions of places like Saudi Arabia, crime scene evidence can be exposed to extreme levels (high and low) of temperature and humidity before it reaches the laboratory.