A motion for a change of venue may be filed by either the state or the defendant. It shall be filed in accordance with Article 521; or thereafter, in the discretion of the court, any time before the first witness is sworn at the trial of the merits. The motion shall be in writing, sworn to by mover or his counsel, and shall contain:
A contradictory hearing shall be held upon the motion.
La. Cr.P. § 621