Sure but mental illness may be a mitigating factor at sentencing with less jail/prison time with mandated therapy, but in the legal system being crazy and being found not guilty due to insanity, the latter meaning you don't know right from wrong. So you can kill, skin, and eat 20 people. If you try to hide evidence of your crime for example, you might be bat shit crazy, but you will be found guilty, because hiding evidence means you knew it was wrong.