"We heard this bloodcurdling scream and turned around, and the guy was standing up, stabbing this guy repeatedly," Caton said from a hotel in Brandon, Manitoba, where he and other horrified passengers were taken.
Caton said the driver stopped the bus when he became aware of the attack and passengers scrambled off. A short while later, Caton said he re-boarded along with the bus driver and a trucker who had stopped to see what was happening.
He said the suspect had the victim on the floor of the bus and "was cutting his head off" with a large hunting knife.
"When he was attacking him, he was calm," said Caton. "There was no rage or, or anything. He was just like a robot stabbing the guy."
The attacker turned toward them and the three men quickly left the bus, blocking the door as the attacker slashed at them through an opening. The three secured the door to prevent the man's escape. Caton said the driver disabled the vehicle after the attacker tried to drive it away.
As the three guarded the door with a crow bar and a hammer, the attacker went back to the body and calmly came to the front of the bus to show off the head.
Cody Olmstead, another passenger, said the man "dropped the head and went back and started cutting the body." Olmstead said the man later use the head to taunt police.
No reports of the killer saying "there can be only one".