Ok, I have read a few more of the posts on this thread now.
I have now another reason why he beat up the grieving mother. Its because he is feeding off an undercurrent of belief in our culture that thinks it is 'understandable' for men to lose control of themselves and beat up women when they are under stress. This legitimises men behaving this way as they. 'can't help themselves'.
Of course, this rationale is nonsense. We all know that normal decent men, who have internalised how wrong it is for men to be violent to women, do not beat up their fellow grieving partner or are violent to their wives and girlfriends when they are under 'life stress'. Only men who already believe it is ok for them to beat up women to relieve themselves of 'bad feelings' do this.
So to posters seeking to 'understand the context' that 'triggered' this assault, look no further than yourselves. The attitudes you are espousing are the ones in our culture that this young man fed off to justify that assault.