La. Stat. tit. 15 § 257
Except as provided in R.S. 15:257.1, whenever it shall appear, upon motion of the district attorney or upon motion of a defendant supported by his affidavit, that the testimony of any witness is essential to the prosecution or the defense, as the case may be, and it is shown that it may become impracticable to secure the presence of the person by subpoena, a judge, as defined in Code of Criminal Procedure Article 931, shall issue a warrant for the arrest of the witness. The witness shall be arrested and held in the parish jail, or such other suitable place as shall be designated by the court, until he gives an appearance bond as provided for defendants when admitted to bail, or until his testimony shall have been given in the cause or dispensed with.
La. R.S. § 15:257