One of the things that scares me about the US criminal justice system is that it relies almost entirely on magical thinking and torture to secure convictions. I don't believe anyone is guilty unless they were literally photographed holding the bloody knife while standing over the body and even then I'll need some convincing to rule out potential mitigating circumstances.
The killer also has a history of domestic violence, is a registered Republican voter and has severe entitlement issues. The tendency to just pump victims full of lead shows they're prone to outbursts of anger due to their deep-seated insecurities and have a world view in which all people are either victims or criminals.