That has very low chance of being tried and nearly zero chance of succeeding. Chris does not meet "not guilty by reason of insanity" in the slightest. You do not just get to commit a vile crime and then claim to be Jesus as a Get Out of Jail Free card. Brian David Mitchell tried more or less this and it dragged things out for years but he's still serving life.
This kind of thing can be a negotiating tool too. Just the prospect of having to deal with Chris for the next five years might bring someone to the negotiating table.
The real problem with NGRI as a plea is the burden of proof is on the defendant. I think this is incorrect for a number of reasons, but whatever. It's an affirmative defense as currently applied, and more or less requires admitting to the facts of the crime, or at least the facts of some crime or lesser crime. If it wasn't a crime, you wouldn't need an insanity plea.
Chris's problem is the only real primary source for any evidence of (legally qualified) insanity would be his own testimony and expert mental testimony by people who have examined him or his records. Examining physicians with a history with the patient are generally given more credibility than single-purpose examiners or people who have simply reviewed the patient's records.
Despite that, they're still just relying on the presentation of the patient himself, so again we're back to Chris.
Meanwhile, there is substantial evidence from the time that Chris in fact was entirely aware what he was doing was illegal, he engaged in it in a ritual fashion every three days, showing premeditation and advance planning, it continued for a period of time, indicating ability to maintain a routine, and he lied about it to others, indicating he knew it was wrong and something to be concealed.
He literally even bought a book to improve his technique at committing his signature crime!
I don't see how an insanity defense can survive evidence of Chris's actual conduct at the time in question.
His name was Carlos Chantor.
HIS NAME WAS CARLOS CHANTOR!