From the Atlanta Constitution Journal story about the murder trial of Brian Nichols, who during his rape trial grabbed a guard's gun and then shot and killed the judge, court reporter and 2 others:
Lead defense lawyer Henderson Hill tells the jury that Nichols has confessed to the crimes in the 54-count indictment but is not guilty because he is insane, a man driven by a delusional compulsion that Nichols described as “a demon growing inside of him.” Hill (no relation to the prosecutor) tells jurors to analyze Nichols. “Part of your challenge will be to figure out what it was that caused a broken psyche to come completely unhinged,” the lawyer says. “Keep your minds open.”
Thankfully the jury didn't buy this defense and found Nichols guilty on all counts.
In some coverage of this case there have been accusations that Nichols was wrongfully accused of rape since Nichols himself made that claim before he murdered 4 people, but his defense attorney in the murder trial conceded that his client was guilty of the rape charges which led to his rape trial.
The defense attorney positioned the rape committed by Nichols after the end of a relationship as supporting evidence for the insanity defense. The problem with this premise is that rape in response to the end of a relationship happens far too regularly.
Nichols' rape victim didn't see him as even potentially dangerous until he ranted jealously against her date shortly before Nichols raped her. But again that lack of warning signs that someone is willing to commit rape under certain circumstances is common. That's a sign of control, rationalized anger and entitlement not insanity.
Unfortunately, most who rape under these circumstances get away with rape without being charged because of the "women lie about rape" mythology which baselessly dismisses the report of rape by an ex as nothing more than revenge for regretted consensual sex if there is DNA evidence and just a bold-faced lie if there is no physical evidence.
Nichols likely expected to face no legal consequences for his decision to commit rape and then felt persecuted when he was rightfully charged for the crime he committed. That's a rational feeling and is supported by the arguments of many rape denialists and rape apologists.
Murder in response to criminal allegations is also far too common and so too is the excuse that the alleged victim is the one responsible for making the murderer "snap." Anyone who sees murder under these circumstances as proof that the defendant has been wrongfully accused is a fool.
This idea that Nichols snapped was disproven by the prosecution showing letters from Nichols to a woman, written before the murders, where he discusses the possibility of escaping. In those letters he also wrote about gaining people's empathy in the hopes of getting the right people on his jury to meet his goal of being found not guilty.
That is rational thinking. What the defense tried to do was to position criminal choices as proof of insanity because of the severity of those actions. People who are rational and legally sane can delude themselves about what they can get away with. That is arrogance, not insanity.
In a phone call to his father, Nichols seems to agree and characterizes the murders he committed as a decision to "stand up for himself." Someone can be dangerously wrong and still be sane and legally responsible for his or her actions.