Week three of my Introduction to Forensic Science course completed – phew! It covered Blood Pattern Analysis and DNA. Again, really interesting, but getting extremely technical this week. For a writer of crime fiction, the in depth details of the sections of DNA used to extract a genetic fingerprint and the methods used is great knowledge to have but not necessarily to bore and confuse readers with. The gory details of blood pattern analysis was much more accessible, however.
Basically, BPA is affected by the angle at which blood is shed, the force behind it, and the surface it lands on. So blood dropping onto a smooth surface from directly above it will form smooth round stains, but at an angle it will be elliptical with a tail (kind of like a comet). There are three categories for your fictional crime scene investigator to know about – drip stains or patterns which are caused by gravity only eg dripping as someone who is injured is running away; transfer stains/patters such as blood on a hand being transferred to a door; and spatter patterns caused by a greater force than gravity eg flying out from the impact of a bullet.