Code of Criminal Procedure §9

(a) If a subsequent application for a writ of habeas corpus is filed after final disposition of an initial application under this article, a court may not consider the merits of or grant relief based on the subsequent application unless the application contains sufficient specific facts establishing that the current claims and issues have not been and could not have been presented previously in an original application or in a previously considered application filed under this article because the factual or legal basis for the claim was unavailable on the date the applicant filed the previous application. (b) For purposes of Subsection (a), a legal basis of a claim is unavailable on or before a date described by that subsection if the legal basis was not recognized by and could not have been reasonably formulated from a final decision of the United States Supreme Court, a court of appeals of the United States, or a court of appellate jurisdiction of this state on or before that date. (c) For purposes of Subsection (a), a factual basis of a claim is unavailable on or before a date described by that subsection if the factual basis was not ascertainable through the exercise of reasonable diligence on or before that date.