Art. 855.  Errors discovered after verdict or judgment of guilty; necessary allegations

A motion for a new trial based on ground (4) of Article 851 shall contain allegations of fact sworn to by the defendant or his counsel, showing:

(1)  The specific nature of the error or defect complained of; and

(2)  That, notwithstanding the exercise of reasonable diligence by the defense, the error or defect was not discovered before or during the trial.