I have a revised theory based on some details I came across, here and other platforms. Theory only. Sherri had a conceal & carry type board on her Pinterest. Husband and family were adamant from the very beginning that this was an abduction. I believe someone was infatuated with her (obsessed/stalking/inappropriate interest for a married woman, whatever you want to call it), and both she and Keith were aware and thus wanted to protect Sherri from this person. Thus, the C&C board on Pinterest. Whether she actually purchased or owned a gun is entirely different (was this ever confirmed??). Perhaps she was just looking into buying a gun, for protecting herself due to this person that has an inappropriate interest in her. Where they know this person from (Best Buy druggie circle, acquaintance, etc) I do not know.
This theory would explain why Keith immediately claimed abduction, because there was already an existing threat to Sherri. Why not put other precautions in place (i.e. why would she go jogging alone if she felt there was some kind of threat to her?); perhaps both Sherri and Keith underestimated person's capabilities or felt "safe" thinking said person doesn't live near or isn't aware of where the Papini's live. There are a lot of reasons people don't take all precautions when felt threatened- case in point, that latest article about the college woman at Shasta College who reported to being followed for quite some time, but never did or said anything about it until recently (source).
This theory would explain why Keith immediately claimed abduction, because there was already an existing threat to Sherri. Why not put other precautions in place (i.e. why would she go jogging alone if she felt there was some kind of threat to her?); perhaps both Sherri and Keith underestimated person's capabilities or felt "safe" thinking said person doesn't live near or isn't aware of where the Papini's live. There are a lot of reasons people don't take all precautions when felt threatened- case in point, that latest article about the college woman at Shasta College who reported to being followed for quite some time, but never did or said anything about it until recently (source).