(CNN) -- As horrified travelers watched, a Greyhound Canada bus passenger repeatedly stabbed and then decapitated a young man who was sitting and sleeping beside him, a witness said Thursday.

"There was a bloodcurdling scream. I was just reading my book, and all of a sudden, I heard it," Garnet Caton, who was sitting in front of the two men, said of the Wednesday night incident west of Portage la Prairie in Manitoba.

"It was like something between a dog howling and a baby crying, I guess you could say," Caton said. "I don't think it will leave me for a while."

Passengers exited the bus, and a trucker who stopped provided wrenches and crowbars to several of them so they could keep the suspect on the bus until police came, witnesses... more