If you write a novel about murder or write about the many ways to kill someone, and a reader uses what you have written as a template for his or her own crimes, you cannot be prosecuted. Just because your murder mystery novel was read and followed like a map for homicide does not mean you are responsible. This is not something that you can be charged with, and here is why.
Fiction Is Not Reality-You Did Not Commit a Crime By Writing
What you write, whether it be a book or song, is not evidence supporting a crime even if the alleged and accused murderer used your works to plot and execute a murder. Your work is entirely fiction, and while you may have done some research to write it, it is not by any means a "how-to book" for would-be murderers, nor are you encouraging people to kill each other. If a lawyer could prove that your novel is the device which caused others to kill, then all lawsuits surrounding the works of Hitchcock, Poe and Agatha Christie would have to be revisited.
If You Are Implicated in a Crime Because of Your Novel
In stranger than strange cases, authors have been implicated in crimes because of what they wrote and how others react or respond to what the authors have written. If you happen to find yourself in that stranger-than-your-own-fiction situation, contact a criminal lawyer right away. Once the lawyer has the facts in the case, he or she can defend you and argue that the charges are absurd and unfounded. Only If you have actually told a fan to go out and commit a crime based on your work are you at fault, and even then the murderous fan would have to prove that you told him or her to do it.
Proving Your Innocence in a Murder Case Your Novel "Inspired"
When more than one murder and alleged murderer claims your novel "inspired" their homicides, your lawyer will have to prove that each of these accused murderers is looking for a way to escape punishment. Additionally, any and all of your messages, emails, texts and social media posts will become public and come under scrutiny of the investigators involved in the case. Since you cannot completely erase everything you have ever written and sent out into the virtual world, you may have to explain any questionable posts and emails you have sent. Be prepared to explain and defend anything the plaintiff's/alleged murderer's lawyer might use to explain how your written words moved others to action and, possibly, murder.