Ichimi no Chichi Special: Who Killed the CA Prologue

Prologue
A week before December The Beloved CA passed by along the corridors in the Third Floor, checking the classrooms in order and the surroundings. Then, She went back to her office, doing her usual business.

As always, the day has ended. Students have tons of homework... Teachers, on the otherhand, have tons of tasks to do for tomorrow and have some things in mind that people can't determine.

The next day, here comes the class suspension. Students cheered, relieved from the hardwork, while the teachers... spent more time planning for the lessons at the same time, planning on how to kill the CA.

After the class suspension, on the following day of classes. Morning, as the early students came they've noticed that the CA didn't appear as she always does every morning, yet they don't even bother to investigate. Later, as more students came, starting the day without the CA, until one student went to the washroom near the office, spotted a broken mirror, shards fell on the floor, stained with blood, a blood trail towards the janitor's closet. Opening it, she saw blood stained on the wall written:
"Tasukette..."
Shrieked, the students and teachers of the third floor rushed in, making a scene.

"What's going on?!" A female teacher asked, got surprised.
"Miss...Bl-blood!" the student who shrieked answered.
"Go to the CA's Office!"
"H-hai!"

Going to the CA's Office, she found out that the CA's dead on the floor, holding a dagger on her hand. The office was a complete mess! Blood splattered all the papers. For awhile, she called the authority.

"MISS! THE CA IS DEAD!!!!"

Once she has mentioned it, the whole batch began to crowd. Then, Ichimi no Chichi entered the scene, used their strength to make their way to the crime scene. Once they've reached it, they stared at the corpse. For awhile, some of them tried to unlock the clues for the murder, while one of them stared at the teachers, smiling to the dead body.

The Girl wondered why are the teachers smiling and what are they up to.

Teachers in charge of each section ordered the students to go back to their classrooms and go on with the subjects.