If he planned to do this (and I believe he did), how would he know his teacher would ask him to stay after class and that she would enter an accessible bathroom versus a staff washroom that can be locked? Was he planning to kill her inside the classroom? What about the other girl who was also getting extra help? Did he plan on killing her too? Did he know she would be there getting extra help?
Maybe he was just planning to find a way to kill her, and the details sort of emerged as he went. Because in the timeline, he exited the classroom after her, followed her --- and she happened to enter the bathroom. He could as easily have followed her to the parking lot, another empty classroom, pushed his way into the faculty bathroom as soon as she opened the door to it, etc.
Isn't it weird that he didn't do anything to wedge the bathroom door closed or keep anyone from entering while he killed her? He had no way of knowing whether another teacher or student would walk in while he was killing her!
And isn't it also crazy that he re-entered that bathroom 9 minutes (wasn't it?) after he killed her, wheeling a huge recycling bin? How did he know that in the meantime, no other girl/woman had entered the bathroom and sounded an alarm? He already knew that he was seen in the bathroom by someone - instead of running away, he STILL came back 9 minutes later, and risked getting caught loading a dead teacher into a recycling bin!
So my thought is that he was prepared to take huge risks that day. And perhaps the fact that she walked into the restroom just chose the spot for him by chance.
I also think that he took her out of the bathroom because he had a fantasy of dumping her and staging her. Why else would he come back for her body once he'd gotten away from the crime scene (bathroom) without getting caught? I guess he could have thought he was buying a little time, but he was willing to risk being apprehended as he trotted all over the school wheeling stuff into elevators and re-entering the scene of the crime, already knowing he was spotted at least once?
Nope, and is exactly my point..a naked man in the student's girl's restroom would strike immediate alarms..hence my entire point.. My point is not questioning would walking in on a naked male in the highschool girls bathroom be no cause for alarm..its the exact opposite, cause for alarm! Jmo.
Immediate instinct of alarm..reaction to immediately turn around and get the hell out of there..alarm bells of something not right, here..instinctive alarm bells many times leading into actions that follow sounding an alarm to alert others who are in a position to check out the situation that you've rightfully just fled..
**Please forgive the limitations that come w/my posting via mobile ATM**
I hate to say this, but no, I don't see anything weird about this girl's actions at all.
Seeing a naked guy's butt and pile of clothes in the girls bathroom (but no screams for help) would probably ordinarily mean either someone was changing clothes and that was really embarrassing to have accidentally walked in on, and should be forgotten immediately, OR that a guy and his girlfriend were having risky afterschool sex - and most teenagers I know would immediately back out of the situation in embarrassment. Like "Yikes! sorry" or "Eww, I'm going to forget I saw that..." or even, "Omg, omg, gross.." and then repeatedly thinking about it and processing it after they got home, before deciding to tell someone.
If there had been screaming? yes, I can see someone immediately sounding an alarm. But a quiet bathroom and a naked guy's butt? Maybe not. And teenagers do have those "alarm bells" in their head, but perhaps don't trust them as much with their peers, on average, as an adult might. Perhaps the idea that accidentally making a huge deal of a sports player who was changing for afternoon soccer practice in an empty bathroom (even the girls bathroom - hey, maybe the guys' bathroom was being cleaned, or his friends jokingly locked him out) -- far outweighed "maybe a serious crime is happening" in the average teenager's head. After all, it's not like they were living in a dangerous place where that would be forefront in their minds.
Also, it's a sad fact that a lot of highschoolers are already having sex or doing sex acts with each other, if you can believe the rumors even within the school itself.
Finally though, and something I've wondered from the first time I read of this poor girl's close call - the teacher's throat was slit, and that should have produced a lot of blood. Depending on the layout of the bathroom, it's possible this poor girl, in her brief second of unexpected vision, glimpsed a naked butt AND something else she couldn't bring her mind to accept. Maybe a splash of blood, or an odd smell. And I think she would be completely forgiven for immediately blocking any further thought of that, or creating a quick mental story that would make what she saw potentially innocent or explainable to herself, so she didn't have to acknowledge anything else. This would IMO be completely understandable.