I have been charged with a crime? Should I hire an investigator?

No, not without going through an attorney. Although an investigator may be very useful to your case, it should be coordinated through an attorney so that you preserve the client- attorney privilege. If at least the reports don't go through an attorney, a grand jury or a trial subpoena can obtain the entire investigator's file, some of which could be damaging to you. When the investigator is reporting to an attorney and assisting the attorney in the rendition of legal services, the material is privileged and exempt from being subpoenaed in most circumstances.