I know that it tends to be a human nature reaction to these kind of events to look for a "reason" a particular thing to hang our hats on and say "that explains why!" - but sadly as humans we have often done some incredably stupid and random things that can't be explained.
That said, I am also of the view that perhaps our lifestyle and something in our world is making people angrier - Road Rage is getting worse, people are getting attacked more, there appears to be more violent crime. It is worldwide - so I can't help but question what is making the world angrier.
I know I used to get insanely angry when on the SAD way of life, everything stressed me and I fired up at the flick of a switch - I am certainly a lot calmer now on Primal/Paleo.
To say that the person did what he did due to bad diet is probably a long bow to draw, but I certainly couldn't argue with a view that a persons diet and lifestyle may have contributed to their mental state.
I definately think the question could be asked "What affect does the food we eat and the lifestyle we lead have on our mood and mental state? And does eating primally help to reduce anger and violent tendancies?"
Starting Weight (11 August 2012) - 117.8 kgs (259lbs)
Current Weight - 94.4kgs (207lbs) (as at 14/01/2013) -23.4kgs (51lbs) lost to date.
Goal Weight - 90kgs (198lbs)
"Worrying is like a rocking chair, it gives you something to do, but doesn't get you anywhere" - Van Wilder