I don't think that he will be acquitted if he pleads insanity. There are several different tests that the various states have adopted to define insanity. Generally, it is a legal question not a medical one. I am not sure which definition of insanity Colorado uses but from my limited understanding of the facts he will have difficulty meeting any of the current standards.
My gut feeling is that Fowler was acting under extreme emotional distress not amounting to insanity. If established, this would reduce the degree of the crime and hence the maximum sentence he could receive after conviction. This defense, if asserted, together with what I can only imagine will be overwhelming evidence in support of it, would be a major flap for the church.
In the meantime, I will continue to . . .
He COULD go the Diminsihed Capacity route (see http://www.legalview.info/Legal-Dictionary/Diminished_capacity/Default.aspx). This could potentially keep him OUT of the psych hands, but allow him to speak to his STATE OF MIND, and the can of worms that would open.
Unfortunately, with a Public Defender, there will not be a vigorously mounted defense. She will do what she can to get a reduced charge, but that is about it.