The longer this goes the use of a knife seems to be really telling. This area of the US has a lot of hunters and people with guns so why would he choose a knife? One stat indicates ID is #4 for gun ownership in the United States. *
Use of a knife over a gun can be significant. It's slower, more physical and more personal. It's also quieter in theory but not if something goes wrong or someone hears something. It can be more easily dropped in a scuffle especially if slippery with blood. he waited until they were in bed (how did he know that though?). Being in bed is more vulnerable but with so many people in the house it speaks to confidence and/or recklessness.
This crime would likely require brute strength, some sort of stealth knowledge. Due to the strength and total callousness I would guess older than college age. Likely a person who has killed before since killing like this would be seriously shocking if it was the first time. And he didn't stop at 1 or 2 victims but just kept going. IMO likely someone with either military or private militia background (also big in NW US). Would almost certainly have to be a hunter. Significant anti social tendencies. Potential for delusional thinking.
One fear I would have is that he is sticking around in the area to keep tabs on the mayhem. Perhaps going out to a place in the wilderness , cabin or hunting spot.
It seems like the Mad Greek restaraunt could be significant since both K and M worked there. Maybe this person ate there and developed a fixation on one or both girls. Servers have to talk to people and be friendly to some extent.
I would want to ask anyone in that area of the restaraunt , or any place across from it, if they saw someone ho was a bit creepy or off putting or who the girls made an offhand comment about. Maybe someone who didn't stick out like a sore thumb but also didn't fit in. Would want to know what is across the street as he would likely be watching them to learn their movements. I would want to know if there was someone who used to hang around who isn't there now.
Ultimately this is a very scary case and I would not be going back there if I was from U of I.
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Gun Ownership by State 2022