Some armchair detectives argue that Harmony Ashcroft stumbled upon a multi-state serial killer who disposed of victims in geological sinkholes common to the Ozark Ridge. The PDF mentions three other missing women from the 1990s whose remains were found in similar red clay. None of those cases were officially linked until the PDF revealed matching soil analysis reports.
If you wish to research this case ethically:
For those just joining the server, here is the summary found on page one of the PDF: