For decades it has become normal to hear about family members snapping and killing multiple loved ones. This theory to me seems most plausible for several reasons.
i believe that the original 911 caller stated no one answered so she used a hidden key to enter the home of the victims. My first clue to this seeming personal is the mention of the key. This statement alone tells us that when she happened upon the home it was locked. She didn't visibly notice any physical disturbances to the windows and or front entrance that may indicate forcible entry. This statement also tells us that she had access to their home with knwoledge of a hidden key... The same key could have been used by the suspect(s) and placed back in place that way it wasn't known immediately how they entered the home.
Another news station interviewed a family member who stated that there were multiple dogs that would have reacted to the suspect(s)... Unless of course the suspects were familiar with the dogs in which they would have no problem handing them a treat and moving on.
The mention of drug "cartel" seems like a far stretch considering there was still evidence of marijuana at the scene... Assuming I am with the drug cartel ...what good is killing an entire family at 4 different locations if I do not take the drugs from the operation.. And if my motive is to prove a point because of wrong doing than how is it I am familiar with an 8 mile stretch, consisting of 4 properties , all related?
One autopsy reported 9 shots to a single individual.. 9 shots. Is that two separate guns? Is that passion? Why shoot someone 9 times if your only mission was to kill them then that was surely done in the first few shots... A crime of passion may unload a weapon and re-load.
The most plausible scenario is "snapped" in a large family in a small rural community.. How difficult would it be to drive down a rural 8 mile stretch, comfortably walk into friends or family's homes, shoot them, and then drive down to the next house and then finally home? The crime goes undetected until 7am and a close relative or friend would know the daily routine enough to know their window.
I think the best question is : Who would have the best motive for driving that 8 mile stretch and killing 8 people? And for what?