Forensic psychology
Forensic psychology has some major roles in a court that bring psychology into a legal arena. The first is "malingering" a defendant is pretending to have a  mental illness, or is lying to the court about his state of mind. A forensic psychologist keeps in mind that a defendant may have a mental disorder but also keeps in mind to watch for signs of deception, or errors in the defendant’s story.  Another job of a forensic psychologist is to investigate the state of mind of the defendant at the time he or she committed the crime. Another is to see whether or not the defendant is able to be charged with the crimes due to his or her mental condition. Another job is to evaluate the defendant to see if he or she is able to be rehabilitated, or if they might commit the crime again.