Normally, it's not helpful for the defendant to take the stand, however, I'm not sure what he had to lose if he did. What if he described what he claims happened? What if he described getting the knife to harm himself and the next thing he knew he heard Jamie screaming? Bizarre yes, but, at least it's a version for them to consider. They could judge his demeanor and his story of why he did this to a person he cared about. Whereas without that version, they only have what snippets he told the police. So, if there is a slight chance they may go for second degree over first degree, what's the down side? Maybe they know more than we do, but I just don't see what they had to lose by putting him on the stand. If the jury finds second degree, then it's a victory for them. Without his testimony or a good diagnosis from a mental health professional, I can't see how they can find second, instead of first degree.