Police charged a man Monday with an attack on a Greyhound bus in northern Ontario that left a passenger hospitalized, just weeks after a suspect was accused of stabbing and beheading a fellow traveler on a Greyhound.

David Roberts, 28, was charged Monday with aggravated assault and breach of probation in the latest attack.

Police said the 20-year-old victim, who was not further identified, was hospitalized with non-life threatening injuries.

Ontario provincial police Const. James Searle said the victim and his attacker didn't appear to know each other and that investigators were trying to determine a motive for Sunday's attack.

Police wouldn't confirm the victim was stabbed but witnesses said the attacker had a knife.

Anita Daher, a Winnipeg author sitting behind the driver on the bus traveling from Toronto to Winnipeg, Manitoba, said Monday that she heard a commotion from the back of the bus and saw a man clutching his chest in pain.

She said Roberts then demanded to be let off the bus before passengers called police on cell phones. Police said the suspect was arrested a short while later.

The attack came less than two months after the gruesome slaying of Tim McLean, 22, on a Greyhound traveling from Edmonton, Alberta, to Winnipeg with 37 passengers. Police said an assailant stabbed McLean dozens of times before severing his head in an unprovoked attack. Vince Weiguang Li is undergoing a psychiatric evaluation to determine whether he is competent to stand trial for the killing.

Passengers who witnessed the latest attack questioned why police put Roberts on the bus.

"I certainly want to know how this happened," Daher said. "I would certainly like to see some security measures put in place.

Ontario Provincial police say they were assisting local officers with the alleged attacker shortly before he boarded the bus. But Searle said he couldn't comment further.

Greyhound spokeswoman Abby Wambaugh declined to comment on the incident.

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