My writing shelf has all sorts of research books. I recently unearthed five (relatively) older books from the Writer's Digest HowDunit series. There are a total of 12 books in the original series, each one focuses on an area of crime investigation.
Just the Facts, Ma'am by Greg Fallis: What does an investigator actually do on the job? What kind of techniques does he/she use at a crime scene?
Missing Persons by Fay Faron: How do the police and investigators go about finding a missing person? Who are the easiest to find, and how and why do they hide?
Scene of the Crime by Anne Wingate: Who's the first person to arrive at a crime scene? What do investigators look for at the crime scene? How is evidence identified, handled and analyzed?
Private Eyes by Hal Blythe, Charlie Sweet and John Landreth: How does someone become a P.I.? How do they run their businesses? And what kind of working relationships do they have with the police and courts?
Police Procedural by Russell Bintliff: What's the police "mindset"? How are officers trained and how do they advance in rank? Who has jurisdiction over whom/what, and what kind of techniques do they use for their jobs?
The other seven in the series (which I don't own) are:
Armed and Dangerous by Michael Newton: A guide to guns and everything that goes 'boom'.
Murder One: A Writer's Guide to Homicide by Mauro V. Corvasce and Joseph R. Paglino: What's involved in murder cases, including accidental homicide and crimes of passion?
Deadly Doses: A Writer's Guide to Poisons by Serita Deborah Stevens and Anne Klarner: The symptoms, reactions and administration of all sorts of poisons, and how investigators analyze and identify them.
Malicious Intent by Sean P. Mactire: What goes on in a criminal's mind?
Modus Operandi by Mauro V. Corvasce and Joseph R. Paglino: What are the nuts and bolts of a murder case? A counterfeiting case? Smuggling? Other crimes?
Amateur Detectives by Elaine Raco Chase and Anne Wingate: How does someone make a citizen's arrest? And how can the amateur sleuth help (or hinder) police?
Rip-Off: A Writer's guide to Crimes of Deception by Fay Faron: What are the ins and outs to crimes like Ponzi schemes, three card monties, charity scams, bait-and-switches and identity theft?
If you aspire to write crime fiction, these are must-haves for your bookshelf!
All original writing and art copyright A. Dameron 2000-2011