You can appeal the case, for a start: that may well provide the "reversible error" that allows the appeals court to remand the case for a new proceeding and/or simply reverse it and dismiss it.You may also be able to sue the investigator and his company (if a private investigator) or the city or state (if he was a police officer) for monetary compensation, if you can show that he wasn't just wrong, but knowingly lied on the stand. You should speak with a criminal defense and/or civil rights attorney right away, based on what you write.