If a child goes all whack-o and kills or seriously injures someone else, that child is guilty, and you - as a parent - have failed that child in one way or another. This kids' mother probably had clues along the way that he was unstable and a danger to society, yet she ignored it because of her "love" for him. That's crap as far as I'm concerned. She should be prosecuted for the murder of this man just slightly below her son who threw the first smack with the golf club. I'm sure that she is grieving for her murdered boyfriend, but she should not brush off her responsibility in this incident.
And if my child did something unthinkable like this, you can bet that he'd suffer the consequences for his actions without my help. I wouldn't retain the best lawyer, I wouldn't pay for his defense, and I wouldn't make excuses for what he did. I would still love him - because that is what a mother does - but I would take full responsibility for my part in his actions, and not make excuses because he "snapped" and that "he was such a nice young man, so I don't know what got in to him".