This is a good prompt. You can say many things. Since we live in a pluralistic world, we can point out that not all people will agree with a single standard of justice. Justice for one person may be injustice for another.
In To Kill a Mockingbird, Tom Robinson was considered guilty. This is what the court of law decided. So, from the point of view of the town, justice was served. Tom got what he deserved. However, from Tom's point of view, as well as that of Atticus, Scout, Jem, and many others, the whole trial was a farce and unjust. The trial to them was more about racism that anything else.
So, the question of justice really boils down to perspective. That said, I do not think we want to say that justice is only about perspective and fall into complete relativism. To get around this, perhaps we can use the philosophy of Wittgenstein who talks about family resemblances. Justice is perspectival but not endlessly so. A large community can define justice imperfectly but sufficiently.