"By Reason of Insanity" is a show where people who have committed crimes, like stealing or hurting others, plead that they were not responsible for what they did because they were crazy or had a mental illness. The show tries to figure out if they really were not able to control their actions because of their mental condition, or if they were just using it as an excuse to get away with their crime. It's like playing detective and seeing if the person was crazy or just pretending to be.