At any time during the trial, the court must declare a mistrial and order a new trial of the indictment under the following circumstances: 1. Upon motion of the defendant, when there occurs during the trial an error or legal defect in the proceedings, or conduct inside or outside the courtroom, which is prejudicial to the defendant and deprives him of a fair trial. When such an error, defect or conduct occurs during a joint trial of two or more defendants and a mistrial motion is made by one or more but not by all, the court must declare a mistrial only as to the defendant or defendants making or joining in the motion, and the trial of the other defendant or defendants must proceed; 2. Upon motion of the people, when there occurs during the trial, either inside or outside the courtroom, gross misconduct by the defendant or some person acting on his behalf, or by a juror, resulting in substantial and irreparable prejudice to the people's case. When such misconduct occurs during a joint trial of two or more defendants, and when the court is satisfied that it did not result in substantial prejudice to the people's case as against a particular defendant

isconduct occurs during a joint trial of two or more defendants, and when the court is satisfied that it did not result in substantial prejudice to the people's case as against a particular defendant and that such defendant was in no way responsible for the misconduct, it may not declare a mistrial with respect to such defendant but must proceed with the trial as to him; 3. Upon motion of either party or upon the court's own motion, when it is physically impossible to proceed with the trial in conformity with law.