If there are legitimate concerns as to your and your family's safety if you are a witness in a murder case (key witness) and there is justifiable belief that your safety as well as your family's safety may be compromised, you need to immediately speak with the district attorney's office about your concerns and see what can be done by law enforcement to secure added protection for you and your family given the situation that you are writing about.In a nutshell, law enforcement in your state has the obligation to protect the people of the state in general, and those under threats of harm directly.