Bloodstains have much useful information that can used to indicate various components of how an event unfolded. This is a foundational principle of bloodstain pattern analysis. Additionally, the source of blood is a focus of DNA analysis. However, there may be more that can be gleaned from bloodstains. Commonly, when we encounter bloodstains at scenes there may be questions as to when the events occurred or even if the bloodstains were part of a previous event. Now there is some interesting research in helping to determine the age of bloodstains.
https://www.sciencedaily.com/releases/2018/06/180620094835.htm