Who is the murderer of School Rule 22?

So it was not Lin Yi who killed the principal, but the evil spirits that existed before. Before this, only Xu Ling died, but what Xu Ling can be sure of is that the principal has crossed over. Then the possibility is left, the evil spirit sealed under the nails of the dead soul.

According to the parchment, the ancestors of the Yao family sealed an evil spirit under the nails of the necromancer, and the seal would be shaken by the blood of the Yao family, causing the evil spirit to escape. According to the clue, the principal's real name is Yao, and he also got the nail of death from Mr. Yao Lao.

Matters needing attention

In Xun's dream memory, she once saw that the headmaster seemed to be hurt. The clue mentioned that Xu Ling's body was holding a screwdriver in her right hand. In Zhang Yuncheng's dream memory, after stabbing Xu Ling, he ran away without even confirming whether he was dead, so he could not choose not to take a screwdriver but to put it in Xu Ling's hand.

In the fact that the headmaster killed Xu Ling, it can be speculated that in the process of killing Xu Ling, the headmaster was probably resisted by Xu Ling, which led to the headmaster's massive bleeding. At that time, in order to deal with the deceased as soon as possible, the principal did not dress himself, but directly crossed the past with a dead nail.

From all the clues and deduction, we can see that the headmaster is an amateur, and he doesn't know much about Feng Shui, so he probably hasn't read the records on the back of the parchment. Therefore, Yao unknowingly used the dead soul nail with blood on his hand, which eventually led to the escape of the evil spirits.