To augment DNA profiling and body fluid identification techniques efforts are being made to increase the amount of information available from a crime scene stain, which includes efforts to identify externally visible characteristics through phenotypic analysis. A key question surrounding crime scene stains is the length of time between deposition of the stain and its subsequent recovery, in that is the stain recovered related to the incident in question or from a previously deposited stain number of weeks earlier? The inability to answer this fundamental question has a detrimental effect upon the successful completion of a criminal investigation. Once a body fluid leaves the body, the oxygen concentration in the environment changes; therefore, it may be that this change could cause a change in the expression of hypoxia-sensitive biomarkers. All samples then underwent quantitative PCR targeting Vascular Endothelial Growth Factor A (VEGFA) and Hypoxia-Inducible Factor 1 Alpha (HIF1A), with B-Actin (ACTB) as a reference gene. A range of linear and quadratic correlation values was obtained from the qPCR data and used to develop a predictive model with a mean absolute deviation (MAD) of 4.2, 2.1, and 5 days for blood, saliva, and semen respectively.

The basic questions that must be answered during the crime investigation is who left the biological evidence and when. DNA profiling can, in most cases, successfully identify the person who deposited the sample, leaving, therefore, as the main concern question about the length of time between deposition of the stain and its subsequent recovery. The research in the present thesis is concerned with development of the mRNA and miRNA analysis for correct assessment of the age of blood, saliva, and semen samples. It is widely accepted that the level of RNA in the sample decreases over time. Therefore, reverse transcription quantitative polymerase chain reaction (RT-qPCR) method was performed to quantity the selected markers and investigate how they degrade as a function of time.