In the case of a convicted murderer, the action or the sin committed is over and done with. It can be repented with the intention of never committing that sin again. He or she can be reconciled to God and receive holy Communion.
If someone has been validly married, obtained a civil divorce and then remarried outside the Church, that person has chosen to act contrary to the command of Christ and the Church. As long as this situation persists, repentance and reconciliation are impossible because the Church has no power to dispense people from the marital obligations of fidelity, unity, and permanence.
If you are divorced and remarried, there is always the possibility that your first marriage was invalid and a way can be found for reconciliation and a return to the sacraments. Contact a priest.