With regard to the missing records, I just read that the detectives said not a single record had survived prior to 1972. Within the past couple of years, I attempted to get a forty year old police report on a different matter. I was told then that no records were available prior to 1972. I asked if I might speak to the Sheriff and was told, "He won't know anything about that - he's new." I have first hand experience in dealing with this Sheriff's Office, and although it pales in comparison to yours, I can somehow relate to your frustration.
What happened to the records prior to 1972? Even if they did "purge," they shouldn't have purged an "open" investigation's records, especially one involving homicide, or any death for that matter. Was there a fire? Records stolen? Damaged? Where are the records?
This should be of concern to the Attorney General's Office.