He's going to use a domestic violence/abusive wife defence, just watching his interview with LE and every chance he got his stories of how abusive Emily was were added too, but occasionally he let slip things such as his throwaway comment that you mess with me stuff happens (not verbatim)
I don't know if there was abuse during the relationship, but we are sure to hear all his story of abuse, and IMO I am willing to accept the premise that everybody can be a victim of domestic abuse so I don't discount his reporting of his abuse, I will wait to see if there is other evidence that reveals this, but most abuse is behind closed doors so he may not have any evidence beyond his word, I do find that a persons phone tends to be good evidence of what a relationship is truly like, as in the privacy of our phones the abuse often is on there in text messages, voice notes etc
I don't think he lost his mind due to her alleged abuse that evening, she wasn't in his face according to him she was in bed, he then chose to get his gun and shoot her twice, not a heat of the moment event IMO then he gets rid of her phone, wallet, glasses and casually cuts her up so he can bury her in the woods, and lies to her parents face