The line crossed
Knowingly supporting false evidence against another person.
Commandment 9 · Tell the truth

A rumour claims that a student cheated. You know the screenshot being shared was edited: you watched it happen. The target is losing friends, and a teacher is about to receive the accusation. The group asks you to back the story so everyone’s accounts match.
Thou shalt not bear false witness against thy neighbour.Exodus 20:16 · King James Version
There is a cost behind every answer. Choose one to examine it.
Knowingly supporting false evidence against another person.
Giving an accurate account and correcting false information you spread.
Do not confuse a confident crowd with a reliable witness. What do you know firsthand?
Separate the case into facts you witnessed, things people claimed, and assumptions. Only one category is firsthand testimony.