The state or defendant may challenge the panel. A challenge to the panel may be made only on the ground that the prospective jurors were not selected or drawn according to law. Challenges to the panel shall be made and decided before any individual juror is examined, unless otherwise ordered by the court. A challenge to the panel shall be in writing and shall specify the facts constituting the ground of the challenge. Challenges to the panel shall be tried by the court. Upon the trial of a challenge to the panel the witnesses may be examined on oath by the court and may be so examined by either party. If the challenge to the panel is sustained, the court shall discharge the panel. If the challenge is not sustained, the individual jurors shall be called.