I have no proof, just speculation, but it looks to me that when DNA evidence started becoming available, that someone decided to eliminate that evidence.
Not sure what the deal was with Mama’s husbands. Those must have been for some other reasons.
It’s said one husband died of cancer, another from diabetes and another from a car wreck. Don’t know if toxicology tests were done or if they left hefty life insurance. One managed to outlive her.
A former President and his wife as serial killers. Now that would make a good movie.....