[QUOTE=Diceman]
Isn’t the legal concept of insanity rooted in old Victorian notions of lunacy? Specifically, the idea that insane people were basically animals who didn’t know right from wrong?
[/QUOTE]
I am not a criminal lawyer, but from what I recall from law school, and from poking around the interent, legal insanity generally applies when the person can’t distinguish right from wrong. In other words, Holmes could successfully claim insanity if Holmes didn’t understand that shooting those people was wrong (perhaps, hypothetically, he believed that, like in video games or movies, they would just come back to life).
I haven’t followed the case closely, but one way to discount this type of defense is to show that the perpetrator had taken steps to avoid detection (thereby demonstrating that he knew what he was doing was wrong, or at least would get him into trouble).
This is distinguished from another concept of legal insanity (generally discarded) which says that a person is legally insane if their actions were the result of an “irresistible impulse”. In other words, Holmes would be considered insane if his mental problems compelled him to kill those people.
This second concept seems more apt to the facts in the case; Holmes was deranged, and his derangement compelled him to concoct an elaborate and murderous scheme. But, as I mentioned, it has generally been discarded, for the reason that it is too easy to escape conviction by showing that one’s behavior stemmed from mental illness. A pretty famous example was the “Twinkie defense” used to defend Dan White (which did not say that twinkies made him kill Harvey Milk and George Moscone, but rather that White’s deep depression led him to binge on junk food and commit murder, both anathema to his normal functioning personality).
In other words, society recognizes that people who do detestable things are not “right in the head”, but we’ve decided not to make that the basis for claiming insanity. It’s too low a threshold.
This is the system in place. There is a separate penalty phase, where the jury votes on whether to impose the death penalty. During this time, mitigating factors (including mental illness) are considered.