who must determine whether a defendant was insane at the time of a crime
Insanity defense The defense is based on evaluations by forensic mental health professionals with the appropriate test according to the jurisdiction. Their testimony guides the jury, but they are not allowed to testify to the accused's criminal responsibility, as this is a matter for the jury to decide. Similarly, mental health practitioners are restrained from making a judgment on the issue of whether the defendant is or is not insane or what is known as the "ultimate issue".[8]
Jury The "petit jury" (or "trial jury", sometimes "petty jury") hears the evidence in a trial as presented by both the plaintiff (petitioner) and the defendant (respondent). After hearing the evidence and often jury instructions from the judge, the group retires for deliberation, to consider a verdict. The majority required for a verdict varies. In some cases it must be unanimous, while in other jurisdictions it may be a majority or supermajority. A jury that is unable to come to a verdict is referred to as a hung jury. The size of the jury varies; in criminal cases involving serious felonies there are usually 12 jurors.