Tex. Code of Criminal Procedure § 49.32

(a) Except as provided by Subsection (b) of this article, a physician may not perform, or assist in the performance of, a postmortem examination or autopsy on the body of a deceased person unless the physician obtains the written informed consent of a person authorized to provide consent under Article 49.33 of this code. The consent must be provided on the form prescribed under Article 49.34 of this code.

(b) If, after due diligence, a physician is unable to identify or contact a person authorized to give consent under Article 49.33 of this code, the physician may, as authorized by a medical examiner, justice of the peace, or county judge, as appropriate, perform a postmortem examination or autopsy on the body of a deceased person not less than 24 hours and not more than 48 hours from the time of the decedent's death or the time the physician or other person took possession of the body.