On the one hand, this dream:
This is a dream of reconciliation between id and superego.
I give priority to primitive impulses and desires and follow the "happiness principle", that is, I take the satisfaction of desires and the greatest happiness as my greatest goal (even if those desires violate ethics and even laws and regulations).
Superego is the internalization of social morality, which contains some lofty beliefs and noble codes of conduct, that is, following "moral principles"
In the dream, that classmate killed two people, which is still a cruel way. I read it and said not to let it out. This is your id impulse.
In the dream, the police arrested her, which was the revision of your superego and the restraint of your thoughts.
On the other hand:
This dream is an evaluation of your classmate or someone with similar nature to this classmate.
Think such people are bad or suspicious. Someone who blames others when they are punished for doing bad things.