If I were in Missy's shoes, entering a dark and presumably deserted building and with a gun out in my truck, the ONLY thing that would draw me further into the building would be hearing my name called. Any other noise would send me back to my truck to fetch my gun or get my phone and call police.I've wondered if SP called Missy's name, if it was a familiar voice, it'd explain why Missy had no fear approaching SP. Just a thought.
If someone called my name under those circumstances, I would likely assume it was a camper who'd arrived early and somehow gotten into the building.
Again, that doesn't prove anything either way. Until we know more, all we can do is speculate based on our own experiences.