So it seems like the teacher was actually trying to collect evidence. Makes sense now that I think about it, even if he testified that there was bullying:
1. The principal wants his fake bully free school.
2. Shiori might not testify due to fear and distrust.
3. He can be framed as a sexual harraser of the video by those girls.
It makes sense why he would go this route as a bulky victim in the past. Teachers wont do shit, classmates wont do shit, school will try to cover it up instead and blame you.
Now this makes me wonder why bully victims never try to do this. Even in modern mangas and manhuas, even thiugh they have phones that would catch the bullies in 4K, and also access to internet, youtube and media, the authors purposely never have them take this route. INSTEAD, they have the victims foolishly confront the bullies with their phone in their hand, and then they get their ass beat even worse.
Anyways, off topic. I undertstand the teacher ways, but i still dilike him. That whole thing was so traumatic for Shiori. Imagine if you felt like the whole world was against you. She even tried to commit suicide. It would have been too kate then. Even if the teacher was there to stop her from jumping in front of the train, she has 100 ways to commit suicide in her Arsenal. Bleach, slitting wrist, poison, doping, etc.