Guilty or innocent?

I was watching the morning news and wondered how a person cannot be guilty of a crime when that person committed the crime? A 22 year old male, a legal adult, uses 3 9mm Pistols and terrorizes a college town. This same male posts a video on YouTube and then goes out and does the deed. The next day the Lawyer for the parents, say what???, steps in front of the cameras and states that the child, say what????, isn't 21 a legal adult??, has Asperger's syndrome, hungh??, and was bullied, so what, and is not responsible for what he did. Say what???? Having looked at that posted video I notice that this person, who is a male, clearly states what he is intending to do. I also note that there is not one other person in the car with him at the time. In other words the male was not forced to do anything. If you are not held responsible for your own actions, you are dead, then I believe your estate should be. In other words you did the crime you do the time. Granted the guy is dead. Apologize to the families for his actions but hold him, not yourself, accountable for any and all actions committed.