Stabbing and Beheading on Greyhound Bus

I am obsessed with this story. I first heard about it at class on Friday night and couldn't believe a week had gone by and I didn't even know it happened.

On a Greyhound bus going through Canada, this 40 year old Chinese guy gets on, switches his seat to the back, starts stabbing the 22 year old Carnival worker (Carni) sitting next to him with a hunting knife. Apparently, he is stabbing him with no emotion, not saying anything - "like a robot." The bus driver stops the bus, everyone runs off, they are holding the guy in the bus and he proceeds to cut him up, EAT PIECES and cut off the head. The police come and he is taunting them with the head. The arrest him and find pieces of body in a plastic bag in his pocket (not sure if it is the Carni or someone else).

I mean, WTF! I keep searching the articles to find out why? What triggered this guy? Has he killed before? Apparently, he had recently immigrated to the US and was working as a custodian and seemed fine. What happened? What is also scary is that I'm on public transportation ALL THE TIME, nearly everyday. I've tried to take the bus on longer trips but did think either the bus was unsafe, the trip took too long, the people were really weird so now I take the train. But, wow, this could happen anywhere.