You can try to get the state police or atty general interested if local police screwed up investigation. Have you talked to the district attys office? Otherwise, you may have to hire investigators of your own but that may not work and could be expensive. Was there an autopsy? There are nationally renowned experts who can review the autopsy and other reports etc for an opinion. You can also try to fins a lawyer to file a civil case against her (like the family did to OJ).