I have tried the insanity defense several times for clients I have represented and it is not easy to prove. To be considered legally insane the defendant has the burden of PROVING that he didnt understand that what he did was WRONG.
Clearly JL is insane by societal standards, you would have to be to do what he did, but that doesnt make him criminally insane when it comes to a defense in a court of law. He knew what he was doing was wrong BECAUSE the night before the shootings he posted on his myspace "good bye friends PLEASE DONT BE MAD AT ME." This indicates that he knew what he was about to do was WRONG and ILLEGAL, which means he cannot be considered insane in a legal sense.
However there is a newish criminal defense that can be used instead of NOT GUILTY BY REASON OF INSANITY, which is GUILTY BUT INSANE, meaning he is guilty of the crime as charged BUT INSANE, this would mean he is not 100% responsible for what he did, but he still understood that it was WRONG and ILLEGAL and such a verdict would put him in the hands of DOCTORS in a medical facility as opposed to prison or death row.
The difference is this, not guilty by reason of insanity would put him in a medical facility and he would have to be RELEASED as soon as the doctors found him to no longer be a danger to himself and others, in the case of GUILTY BUT INSANE, he would be sentenced to LIFE IN A MEDICAL FACILITY and even if he did improve and was no longer a threat to himself or others, the doctors would have no legal requirement to release him back in to society.