Crime clock – Analytical studies for approximating time since deposition of bloodstains

Bloodstains discovered at crime scenes can provide crucial information to an investigation. By obtaining a DNA-profile from the bloodstain, it can be used to link someone to a crime scene, which can corroborate or dispute a witnesses' statement. However, the analysis of bloodstains is still not able to answer a key question to investigators; how much time has passed since the criminal event occurred? In addition, an equally important aspect of crime reconstruction is the ability to determine which bloodstains are relevant to the crime based on time since deposition. Despite the extensive research that has been done over the last century, there is still no definitive answer to this question. This review gives an overview of the work that has been done to tackle this momentous issue, from the first attempt in 1907 to the use of smartphones for bloodstain analysis in recent years. Emerging new techniques that are rapid, non-contact, and non-destructive show the most promise for being implemented into forensic casework. However, there are still hurdles that must be overcome before methods for estimating time since deposition of bloodstains will be accepted in the court system.