Yeah your right, actually god is the only one to punish the sinner, He is only one who take away the sin from every person, He know what should do to that person eventhough that person a sinner, he can forgive their evenif their are a huge sin and that person apologize for what they done to their fellow.

We dont have power to punish a person because we are a person also we are the same level to the eye of our Lord God. Be scared for what you doing to our fellow because we something more than they did.