I know this has kind of been resolved but I would not advise anyone to plead insanity. First of all, whilst the Macnaughten rules have been criticised, it is not as easy to meet the requirements as thought. Secondly, it's an admission of sorts, and if you don't meet the requirements, you are basically pleading guilty. Thirdly, if the jury accepts the insanity plea, rather than serving a finite term, you can be placed into an institution indefinitely (for a charge that is not murder, the judge has some discretion).
It's difficult to know what to say (like BG, I know some of the family, albeit in a small way). My heart goes out to them.