A crazed knifeman decapitated a bus passenger and then held up the head for the other passengers to see, according to witnesses.
They said the attacker stabbed the victim up to 50 times and after severing his head he began methodically carving up the body as passengers scrambled to get off the Greyhound bus - which was traveling from Edmonton to Winnipeg in Canada.
Authorities declined to name the victim but tributes have been left on Facebook for Tim McLean, aged 22, from Winnipeg.
A friend said: "All I can remember is good times with Tim, I will miss that, but he's in all our hearts.' Another said: 'RIP buddy. Only the good die young."
Police arrested the man when he broke a window and tried to escape from the bus by jumping out.
Passenger Garnet Caton said the victim - believed to be sleeping at the time - was stabbed by the man sitting next to him.
"We heard this bloodcurdling scream and turned around, and the guy was standing up, stabbing this guy repeatedly, like 40 or 50 times."
Mr Caton said the bus stopped but the attacker remained on board.
"When he was attacking him, he was calm ... like he was at the beach.
"There was no rage or, or anything. He was just like a robot stabbing the guy."
Mr Caton said he, the bus driver and a trucker at the scene re-boarded to see what was happening.
He said he saw the suspect had the victim on the floor of the bus and "was cutting his head off and pretty much gutting him."
They quickly disembarked and braced themselves against the door to prevent the attacker from leaving while they waited for police to arrive.
"We put our bodies up against the door, waiting for him to come out ... and he went back and brought the head to the front and pretty much displayed it ... and dropped it on the ground in front of us," Mr Caton said.
Fellow passenger Cody Olmstead said the man "dropped the head and went back and started cutting the body back up."
Mr Olmstead said the man later taunted the police and dropped the head in front of them.
Police cover up the front windshield of the bus. Passengers told how the killer dropped the severed head there
Greyhound spokeswoman Abby Wambaugh said 37 passengers and one driver were on the bus.
Public Safety Minister Stockwell Day called it a "horrific" incident, but did not discuss details of the attack, saying he did not want to jeopardize the investigation.
"We want to make sure that the process is followed as aggressively as possible, a full legal process, and the perpetrator is definitely dealt with the full force of the law," he said.
Mr Day called it bizarre and extremely rare: "The horrific nature of it is probably one-of-a-kind in Canadian history."One more copy and paste job next.