I really liked your post: keeping close to all facts known, logical.
I agree with a lot you said, but i disagree/getting confused with the killer's escape part.
I agree that the trigger of this was K. Seems logical, she already left the town for good, certainly a lot of people were aware of her plans to relocate across the country and she never made secret out of it (her ad on social media to sale her old car, for example, clearly states she is going away and not planning to return). She did not suppose to be in Moscow, Idaho on that night. She came to show her friends the car she just bought so a lot of people must be taken by suprise when they saw her as she walked in Corner Club that night.
Perhaps, that surprise gave steength to K. admirer to try his luck that night. Only to be turned down, as obviously that admirer were not with the girls when they went to buy food later on. I agree with this.
At the sane time, K. and M. went to a place with much higher risk to meet and attract someone who later would atrack and kill. The trigger for this attack must be somewhere there.
And that explains why the investigation focused on K. and M. movings and whereabouts that night. Besides, X. and E. were in much safer environment that evening, at a party with people most of whom they knew very well.
I am not sure the guy is a student, his actions speak of more mature person, for example someone who can handle own rage at front of others but release it in full with vulnerable. This points to mature person with certain level of responsibilities in their job. They cannot handle rejection in either general or in that period of time in their lives.
I agree that he wanted to teach K. a lesson that night for whatever reason he thought justifies his perception of his right to teach and punish others.
He must have been somehow familiar with the complicated layout of the house prior to attack. If he had long term crush on K. as you suggest and I agree with, then he could have watch the house for a while, not necessarily planning to attack, just to watch her. He might have been on one or two parties there, as he would have tried to get close to her. Or he was in the house in other function - delivery, maintenance jobs, property management, street maintenance. You would never get to that neighbourhood if you do not have/want to go there.
With revelation that both girls died in the same bed, the motives of the killer as we discussed them prior to knowing this, need to be altered, too. I agree with your explanation how the attack has happened and why 4 young innocent people died that night.
He may did not plan to kill 4 people.
But, he had a military type knife with him, prepared to be used. And that points towards planning to hurt mission. Planning to kill, if the need to or opportunity arises. If he was just planning to teach K. a lesson, not killing others, he would have left the house the moment when he heard E. or X. coming out or getting disturbed. But the killer did not hesitate to attack, kill and carry on with killings. He was mentally, psychically and instrumentally prepared to kill.
That points to much better organised, focused, merciless person. Person whose basic instinct is to attack and kill, not just to punish. That is another reason why I am not sure he is a student, but more mature man. For some reasons I think he is 32, plus minus 1 year. Do not ask me why. My perception of mature physically but still immature mentally man.
The escape route is a story on itself. He was dripping blood. Even if he washed his boots and clothes somewhere in the house, he must have dripping blood and blooded water whenever he went.
What puzzles me if why the surviving girls did not notice blood drops on the second floor, there must have been a lot, leading to the kitchen sliding door.
There must have been blood around the door of E. and X. bedroom, where the killings started. That was also not spotted, so someone would go ahead and immediatelly call the police, not friends? Strange.
Handling the dog and silencing him without harming is also a telling story. I had a dog myself, they sense when their owner is in danger and would wake up half of the city barking. It takes a lot of knowledge and experience to handle the dog not to bark when their owner and other people are attacked. Dogs sense blood, it is in their instincts. So, the killer may have a dog himself or he used to have dog, he may be training dogs, working in dog centers or in vets surgery. Thinking of how delivery and dog might be linked, how about delivery of dogs food? Where K did order the dog food from?
