Speak.

"She was new to the school, why would anyone do this to her?" A pause. For a second or a minute, that didn't matter.
"Well, someone say something! Obviously we can't just leave this to the police!"
"But what if she really did just commit suicide? What if she really did just hate her life? Robin, you're just taking this too far, lay it off."
"Do you really want to get mingled in this? Robin, use your head! Look at what you're doing!"
You walk away.
They didn't care.
Someone just died, and it was up to you to find the killer, before they found you.