This attack occurred near the back of the bus, which was pretty empty. The driver, a truck driver and one of the passengers went back on the bus to stop the attacker, this is when they witnessed him decapitating the victim. When they got on and saw that the victim was clearly dead, the attacker immediately moved to attack them, and all three wedge themselves against the door and kept it closed as the attacker attempted to force or stab his way through it. Apparently, when he gave up on trying to get out, he tried to drive away and the driver used and immobilizer to stop him, Then the attacker went back, finished decapitating the head, and brought it to the men holding the door shut to show it to them.
Having been on a few of those long haul bus rides, and especially with this route (which was a very easy drive - all prairie, along the main highway that crosses the country) my experience was that there were few able bodied people of the stock likely to intervene. Usually Greyhound rides are mostly those who either do not drive, or do not own a car: i.e. elderly people (predominantly older women), young people, and the very poor. The route is half the price of a plane ticket, but more than triple the time.
Since I'm bringing us all down, it's time for a happy side_show story about a Greyhound trip I took, because for me, travel is always a little bit magical. Road stories are always about both the inward and outward journeys, so I hope my telling won't be too tinged by what's happened. Please remember this is a story from 5 months ago, well before these horrible things. I'll post it separately from this post, since it's pretty long. It'll take me a while to type out, but I'll be back.