Jade,
Yes, I pictured it that way too. IIRC, SM was about 150 feet away from Kyron last time she saw him at 8:45. And the witness who saw Kyron at 9 :00, I remember reading that this witness supposedly saw Kyron at the door of his classroom. ITA about that stairwell,and the blue exit door. It is very close to the south parking lot of the school.
I wonder if Kyron's classroom door was open when the unidentified witness saw him ? I also wonder how other people didn't see him by the classroom door at that time ? Was his teacher inside the classroom then ? Most importantly, who was with or near Kyron when he was near his classroom door at 9 :00 ? If that witness is a child ( and I think it's a classmate), they could be in potential danger if they saw someone with Kyron at that point...
All JMO