Do you do psychology at A level? If not, try looking up forensic units from A2 level. It contains topics like profiling criminals based on the evidence they leave at a scene (top-down typology). That kind of stuff is used by the FBI and there's lots of controversy surrounding how useful it is at actually identifying a criminal, so it may be a good place to start.
Alternatively, if you're interested in the techniques used, try looking up methods such as bloodstain pattern analysis or DNA sequencing, and talk about how they are employed (this can take about half of your EPQ) before moving on to evaluating them compared to other methods, or just generally (e.g. how widespread, how valid etc.) Hope this helps!
Source: Psychology A2 student and should be on track for full marks on a biology-based EPQ