(a) A district attorney may not represent the state in a criminal case in which the attorney has been, before the attorney's election, employed adversely to the state.
(b) A district or county attorney may not:
(1) be of counsel adversely to the state in any case in any court; or
(2) after the attorney ceases to be a district or county attorney, be of counsel adversely to the state in any case in which the attorney has been of counsel for the state.
(c) A judge of a court in which a district or county attorney represents the state shall declare the attorney disqualified for purposes of Article 2A.104 on a showing that the attorney is the subject of a criminal investigation by a law enforcement agency if that investigation is based on credible evidence of criminal misconduct for an offense that is within the attorney's authority to prosecute. A disqualification under this subsection applies only to the attorney's access to the criminal investigation pending against the attorney and to any prosecution of a criminal charge resulting from that investigation.