Blood, saliva, and semen are some of the forensically most relevant biological stains commonly found at crime scenes, which can often be of small size or challenging due to advanced decay. In this context, it is of great importance to possess reliable knowledge about the effects of degradation under different environmental conditions and to use appropriate methods for retrieving maximal information from limited sample amount. In the last decade, RNA analysis has been demonstrated to be a reliable approach identifying the cell or tissue type of an evidentiary body fluid trace. Hence, messenger RNA (mRNA) profiling is going to be implemented into forensic casework to supplement the routinely performed short tandem repeat (STR) analysis, and therefore, the ability to co-isolate RNA and DNA from the same sample is a prerequisite. The objective of this work was to monitor and compare the degradation process of both nucleic acids for human blood, saliva, and semen stains at three different concentrations, exposed to dry and humid conditions during a 17-month time period. This study also addressed the question whether there are relevant differences in the efficiency of automated, magnetic bead-based single DNA or RNA extraction methods compared to a manually performed co-extraction method using silica columns. Our data show that mRNA, especially from blood and semen, can be recovered over the entire time period surveyed without compromising the success of DNA profiling; mRNA analysis indicates to be a robust and reliable technique to identify the biological source of aged stain material. The co-extraction method appears to provide mRNA and DNA of sufficient quantity and quality for all different forensic investigation procedures. Humidity and accompanied mold formation are detrimental to both nucleic acids.
Keywords: Body fluid identification; DNA/RNA co-extraction; Degradation; Forensic science; STR profiling; mRNA profiling.