Forensics: A Guide for Writers by D.P. Lyle, M.D.
This reference guide is a necessary tool for any writer needing to know the basics of forensics. It discusses DNA, autopsies, fingerprinting, and much more. I really enjoyed reading about the real-life case files and the history of the forensic system.
I learned more than what I wanted to, however, and I say this regarding the autopsies. After reading this section I avoided food for a while. I did, on the other hand, ingest new information that has become essential to my writing.
This is one of the main reasons I constantly harp on the need for us to do research. For example, if you are writing a scene that includes a character in ICU, you will need to know what machines are used and the rules associated with that floor. The reader will have a better sense of being there.
So take that extra time to read up on the subject you are writing about and take lots of notes!