A 40-year-old man is in custody in Manitoba after a young man was stabbed — and, witnesses said, decapitated — aboard a Greyhound bus travelling through the province overnight.

Police officers spent Thursday examining a Greyhound bus where a passenger was reportedly stabbed and decapitated late Wednesday. (CBC)The RCMP would not confirm the reports of beheading, saying only that a stabbing took place around 8:30 p.m. CT on an eastbound Greyhound bus on the Trans-Canada Highway about 20 kilometres west of Portage la Prairie.

The suspect, believed to be from outside Manitoba, was arrested early Thursday morning after a standoff lasting several hours and remains in RCMP custody .

Charges have not yet been laid, and the suspect has not yet been interviewed, said RCMP spokesman Staff Sgt. Steve Colwell, adding that he could release no further information on the investigation.

The RCMP declined to identify either the suspect or the victim.

Thirty-seven people were aboard the bus en route to Winnipeg from Edmonton.

Colwell said the "brave" behaviour of the passengers and driver probably prevented anyone else from being hurt.

"It's not something that happens regularly on a bus," he said. "You're sitting there enjoying your trip and then all of a sudden somebody gets stabbed. I imagine it would be pretty traumatic … the way they acted was extraordinary."

Victim 'just a kid': witness

Passenger Cody Olmstead, 21, told CBC News he had smoked a cigarette earlier in the trip with the victim, whom he described as a man in his late teens or early 20s. The victim got on the bus in Edmonton, he said.

"I never took the time to know him, but he seemed to be OK, right, just a kid," said Olmstead, a Nova Scotia man who had been taking the bus from Alberta to Montreal.

"He just said he was going to Winnipeg … going home, that's where he was from."

Garnet Caton said he heard a 'blood-curdling scream' and turned around to see a man repeatedly stabbing the passenger sitting next to him. (CBC)Garnet Caton, who was sitting in the seat in front of the victim, said he saw the attacker stab his seatmate, a young man sleeping with his headphones on.

Caton said he heard a "blood-curdling scream" and turned around to see the attacker holding a large "Rambo" hunting knife above the victim, "continually stabbing him in the chest area."

"He must have stabbed him 50 times or 60 times," said Caton.

"Like, just everywhere, arms, legs, neck, chest, guts, wherever he could swing it, he got it," said Olmstead.

"It looked kind of like a scuffle or an argument, you know, and then somebody's, like, 'Knife! Knife! Run!' so I was running up the alleyway, slapping people telling them to get going, move, get off the bus. I got pushed over, some lady got pushed over, I was just making sure everybody was OK, and we all got off the bus," said Olmstead

As panicked passengers fled the bus, "the attacker was over top of the victim … continually cutting him. I think the victim was gone at that point," Caton said.

Trio tried to check on victim

Caton, the driver and a trucker who had stopped at the scene later boarded the vehicle to see if the victim was still alive.

"When we came back on the bus, it was visible at the end of the bus he was cutting the guy's head off and pretty much gutting him up," said Caton.

The attacker ran at them, Caton said, and they ran out of the bus, holding the door shut as he tried to slash at the trio.

When the attacker tried to drive the bus away, the driver disabled the vehicle, Caton said.

"While we were watching the door, he calmly walks up to the front with the head in his hand and the knife and just calmly stares at us and drops the head right in front of us," said Caton.

"They did an awesome thing, holding him in there, because if not, what would have happened?" said Olmstead.

RCMP crisis negotiators communicated with the suspect for several hours while he was on the bus. Around 1:30 a.m., he attempted to jump from a bus window and was subdued and arrested, RCMP said.

Acted 'like he was a robot'

Caton described the attacker as surprisingly calm. "It was like he was at the beach or something. There was no rage in him. He wasn't swearing or cursing or anything. It was just like he was a robot or something."

The suspect remained on the bus for several hours and was arrested around 1:30 a.m., RCMP said. (John Woods/Canadian Press)Police cruisers arrived about 10 minutes after the attack began, he estimated, and officers began directing passengers to school buses to take them to a hotel in Brandon.

"While we were waiting on the side of the road, [the attacker] was taunting the police with the head in his hand," said Caton.

Caton described the attacker as appearing "totally normal" earlier in the journey, even chatting with a young woman as he smoked a cigarette during a break.

But when he got back on the bus, he moved his belongings from the front to a seat beside the victim in the back and about 20 minutes later began attacking the man, said Caton. "He didn't say anything to the victim at all," said Caton.

Counsellors, chaplains aid passengers

A six-year-old and other children were among the passengers who saw the horrific incident unfold, said Caton.

"It was pretty traumatic," he said, adding that some passengers said they have been unable to sleep or eat since it happened.

"It's disturbing," Olmstead agreed, adding that images of the previous night haunted him when he tried to fall asleep early Thursday morning. "I closed my eyes and I seen him in the window there, just like a madman."

Bev Cumming, head of acute care services for the Brandon Regional Health Authority, said chaplains and psychiatric nurses have been working with dozens of passengers on the bus since they arrived in Brandon.

"When you see something as horrifying as that, the brain locks on to those images. It's very difficult to release those images," Cumming said.

"The assistance that people will get will be along the lines of coping in the immediate phase, learning what to do to reduce the profound effect this experience will have."

Tim Sen, president of Trauma Management Group, which offers counselling and post-traumatic support in Ontario, said it will take time for bus passengers to come to terms with what they've seen.

"They will experience very, very vivid flashbacks of that occurrence. Those will usually dissipate over a period of time, but right now it's going to be very vivid [as] they're still dealing with the shock and processing this horrific event," he said.

"There's not a right or wrong way to go through this. Some people will still be in shock and being very flat in presentation, like nothing's happened. Other people may not get out of bed and not want to move for a while, or be having what we call very acute [responses], so they'll be maybe crying and not wanting to calm down at all. Everybody's going to go through this very difficult journey in a very different way."

For children on the bus, Sen said, the response will depend on the age and maturity of the child. Generally, the key message caregivers should try to convey is that the situation is over and the child is now safe.

If intense feelings and emotions and symptoms such as flashbacks don't subside within a few months, Sen said, the passengers should consider seeking professional help.

Investigation is in 'full motion': minister

Public Safety Minister Stockwell Day commented on the killing, saying that like most Canadians, he was horrified to hear witness accounts of the homicide.

"The horrific nature of it is probably one of a kind in Canadian history," he told reporters late Thursday morning in Lévis, Que.

The minister said he didn't want to say anything that would compromise the investigation, but "I can assure people that everything is in full motion and momentum to getting to the bottom of this incident."

Questioned about whether weapons regulations should be put into place for buses, Day said it would be premature to look at such precautionary measures but added that the legal process will be followed as "aggressively as possible."

The union that represents Greyhound drivers says the company must move to improve its security measures.

"All we can do is physically observe the individual's behaviour, but obviously the item of destruction got on the bus somehow, and if it was visible to any driver, he would not have boarded the bus just for that simple reason," said Jim Higgs, a spokesman for the Amalgamated Transit Union.

"There has to be some reactive measures taken, whether it be metal screening, or whether we design differently our loading policies at various depots [so] you have to funnel down a chute as your only way onto the bus…. At major terminals, I really believe now we have to do something — not only that, we have to be investigating carry-on luggage and certain things like that."

Greyhound spokeswoman Abby Wambaugh said the company is examining security on buses.

"We are working with Transport Canada to review inter-city bus security," she said.

"Due to the rural nature of our network, airport-type security is not practical for bus travel. It's just a completely different system."

With files from the Canadian Press