Go to the police station and request to see the police report and any/all statements taken. There may be photos - I gasp to think of viewing them. You will have the names of the investigating officers and you can talk to them. They aren't your enemy. You will find out what tests were performed, etc. You can request a copy by mail, of course, with a FOIA request. You can find the format online. There will be a fee for the copies. I know you are troubled by your aunt's behavior. However, a shotgun blast in a suicide is going to look quite different than one from the doorway and it is very likely the inconsistency would have been noticed by the investigators. You can get a copy of all the pleadings filed with the court for the succession. This includes the will and accounting for the disbursement. If it looks like forged signatures, well, you might be on to something. When you have all the information and you still believe that your father was murdered, go to the DA's office with all of it, neat and in a folder and present your case to him/her. Your aunt will be none the wiser.