Defending a killer

Your first big case is a multiple murder. As defense attorney representing the killer, you have come to the realization that he really did break into couple’s home and tortured them in the course of robbing them of jewelry and other valuables. He has even confessed to you that he did it. However you are also aware that the police did not read him his Miranda warning and that he was coerced into giving a confes without your presenc. What should you do? Would your answer be different if you believed that he was innocent or didn’t know for sure either way? What ethical judgment(s), moral rules and ethical systems can be applied in this situation? In 75-150 words.