And then it hits me.
Okay I just realized something. I've been bitching in my head at people who have the boys setting houses on fire to "hide" bodies they've killed, usually a Supernatural thing that didn't dissipate but on one occasion people. Don't ask.
Anyway, I can forgive that though because what happens when someone dies in a fire isn't common knowledge, at least I don't think it is.
However. I have just realized that unless Mary and Jess and anyone/everyone else who died the way that they did had their bodies completely destroyed, and I mean not even bone left unless it's a pile of ash, there is no way their deaths could possibly be ruled "accidental" or caused by the fire.
When somebody dies in a fire the muscles in their bodies shorten and shrink up and they curl into a fetal position. That's one of the ways they know if the fire was likely to be arson, if there are any bodies inside that are in any position but fetal then that means the person was dead before the fire started.
Mary and Jess were in a rather unusual position against the ceiling, they were very... akimbo? Head up, arms out and lowered much like this: / | \ with the legs very awkwardly splayed (almost like the bottom half of a swastika, which BTW is a protection symbol). Personally I always thought, and still do think a little, that the incredibly awkward positioning must mean something. The bodies were obviously "frozen" that way which means that unless The Demon unfroze them that's how they were when they were killed.
The fires started on the ceiling, so chalking them up to "electrical fire" wouldn't be too far of a leap and would be understandable. Especially if there are ceiling fans or lights or anything right up their by them.
If there's any flesh left on the bones after the fire then finding the gaping wound in their abdomens (Another thing that must be symbolic) would be easy and the death would be ruled a homicide and the fire would be ruled an arson.
If there's no flesh or gooey insides but the bones are left and not curled into a fetal position then it would be ruled a homicide and the fire would be ruled an arson.
Honestly, the only way I see John and Sam not being arrested for murder would be if The Demon released his hold on Mary and Jess after they left. Then the women would fall, and they would still have to be alive for this to work, and they would have to burn to death before they bleed to death. And then all the flesh would have to burn from their bones and all their organs would have to liquidate so as not to show the abdominal wound.
The only problem with that is that the fire started directly behind the women and so the odds are that they were burned with their muscles and joints frozen in that position.
But then again, that's just my rambling thoughts.