Tex. Code Crim. Proc. art. 11.59

An applicant may obtain the writ of habeas corpus a second time by stating in an application therefor that since the hearing of the applicant's first application important testimony has been obtained which it was not in the applicant's power to produce at the former hearing. The applicant shall also set forth the newly discovered testimony; and if it be that of a witness, the affidavit of the witness shall also accompany the application.