Well, he obviously has mental issues but I don't think the insanity plea will work. It wasn't like he just flipped out for a few minutes and beat someone to death. This whole event had been carefully planned and deliberated. Any crazy antics he is trying pull now are just him trying to fake it...
Yeah, but the insanity defense isn't going to wash because of the extent of premeditation, unless they can show he was seriously reality impaired the whole time. Now, considering the guy was a neuroscience major...
Whether he pleads insanity or not he'll end up segregated and kept in the psycho section of the prison anyway. Jeffry Dahmer got killed with a mop, I believe, while segregated. Thus Holmes could be taken out too, and whatever prisoner/guard does it should win a widescreen TV at a minimum.