When Jesus was asked how many times do we forgive He said 70 times 7, which really meant always forgive. Jesus forgave right up to the cross that they nailed Him to. He loved and forgave the ones who killed Him.
I was acquainted with a man I won't name who was convicted and sent to the electric chair for raping and mutilating two women. He was under the influence of drugs at the time, but that's no excuse. However, while he sat on death row waiting to be executed he came to know Jesus Christ as his Savior. He spent the next eight years telling many of the men he came in contact with about Christ. God used him to bring other men to Him. He eventually went to the chair, but I expect to see him when I reach heaven. He was forgiven by God, even though humanity will probably never forgive him.
God is just and fair. He will do what's right. We must obey Him and forgive one another always whether, in our eyes, they deserve it or not.