Unforgiveness is a strong acid, that knows no container; hold it in your heart and it will destroy you. It's really silly --- if a person MEANT to hurt us, then we give them the power to hurt us over and over again (and they do). No one deserves that power.
And if they did NOT mean to hurt us, then we're angry over something they did not mean. Equally silly.
So release them to God; it does not absolve them from their crime, but we no longer hold them to account. If they repent in the future, God forgives them; if they do not repent then He judges them. It's no longer our concern, for we belong to Him and He is our source, and our joy.