What am I feeling? At first, alarm bells are going off with the guy starting to act like a psychokiller but after rereading, I started to get annoyed with the woman. Why is she so trusting? Then I thought: She's too trusting, not because she's some kind of innocent, naive type who trusts everyone (which again, would contradict her recent bad experience, if it were true) but because she's faking it. She's a "Girl Scout" who looks capable and fit but was defeated by how to lower the ramp of the truck? I think a real Girl Scout would know how to figure things out, if she didn't find out ahead of time. No, I'm thinking she's an undercover cop or private detective--and that's why she doesn't have a real house-sized bunch of stuff and would also explain the apparently contradictory aspects of her character.
No way does a woman who's on her own and feeling vulnerable or as if she's escaped a bad situation, move into a neighborhood where there has been some horrendous crime and just accept all this help from a total stranger--also from one who has an oddly opaque way of talking, not to mention a sudden bleeding cut right before she "discovers" the boxcutter is missing.
The third person objective point of view here, and your discussion of POVs,* made me think of some of Agatha Christie's books in which she uses third person limited--we follow the murderer him- or herself in seeing what they do and SOME of what they think. I always found this technique a bit unfair--of course, the murderer would actually be thinking of the situation--but in a way, it was a challenge to figure out what thoughts were being left out and to try to get clues from the person's actions alone.
So after my rereading, I'm leaning toward the idea that the woman is some sort of person on the side of justice, who posed as a woman on her own in order to attract the predator who caused the crime we still know nothing about except that it involved a family.
I even flirted with the idea that she might be the murderer herself, but "Scotty" is giving us plenty of reasons to be suspicious of him. You commented earlier on names that are diminutives/nicknames sounded more folksy. To me, when an adult man has a -y name--Bobby, Tommy, whatever--it has an immature sound as of someone who never really grew up, though I know it can be a cultural thing and mean nothing of the sort. You pointed out that "Scotty" mentioned the desert as having thorns, which in the context of events sounds to me like someone with a chip on his shoulder.
Reading the guy's actions, it certainly seems like he locked the front door to keep intruders out for a nefarious reason, and that he rushed to conceal the boxcutter on his person, not having time to close the blade first and thus cutting himself. The fact that he doesn't seem to feel any discomfort is also telling. Then I questioned those assumptions and thought--What if he's a disturbed guy but not a murderer? What if he grabbed the boxcutter to harm himself? and hid it when he heard her coming back. But then why would he lock the front door?
I'm rooting for the solution that the woman is a private eye, master of karate type, with several weapons on her person, and quite able to defend herself--Why otherwise would she keep turning her back on this laconic stranger?? And of course I like when my guesses turn out to be correct!
*POVs did not bother me--in fact, I didn't notice it. It's correct to tack an -s on to the end of an acronym to make it plural, so no need to worry about "points of view" when it's spelled out because it wasn't.