Estimating the time that a biological trace (such as blood, semen or saliva) was deposited at a crime scene can aid the investigators immensely when trying to reconstruct the crime. Knowledge about trace timing allows decisions to be made regarding whether the identified donor could potentially be the perpetrator, and may also help to find potential eye witnesses or additional suspects.
Timing forensic samples can be seen from two aspects. One side addresses the length of time a sample was present at the crime scene (hours, days, weeks, months etc), whereas the other determines the time point (the time of the day or night) a trace was deposited at a crime scene. The first aspect we investigate by trying to understand time-wise degradation processes of biomarkers. We are searching for biomarkers with different (but reliable) degradation patterns that may be useful for relative age estimation of samples. The second aspect we are approaching with the help of chronobiology. We are searching for circadian biomarkers that show sufficiently large concentration differences within the 24h day/night period and at the same time are not influenced by in vitro degradation processes. In principle this may allow investigators to estimate the time at which a sample left the body at the crime scene.