After the commencement of a prosecution, the defendant or the attorney for the Government in the USA may file a motion for a hearing to decide the mental competency of the defendant.
Prior to the date of the hearing, the court may order that a psychiatric or psychological examination of the defendant be performed, and the report of such psychiatric or psychological report has to be filed with the court.
According to the US Code, "A finding by the court that the defendant is mentally competent to stand trial shall not prejudice the defendant in raising the issue of his insanity as a defense to the offense charged, and shall not be admissible as evidence in a trial for the offense charged."
The US Code also observes that "A psychiatric or psychological examination ordered pursuant to this chapter shall be conducted by a licensed or certified psychiatrist or psychologist, or, if the court finds it appropriate, by more than one such examiner."
(More: http://www4.law.cornell.edu/uscode/html/uscode18/usc_sup_01_18_10_III_20_313.html)
| 
