A suspect is due in court in Sault Ste. Marie, Ontario, today following an attack on a Greyhound bus en route to Winnipeg on the weekend from Wawa, Ontario.

Passengers who saw a man attack a 20-year-old fellow passenger on the bus are demanding to know why police put the alleged attacker on the bus in the first place.

Anita Daher, a Winnipeg author sitting behind the driver when the attack occurred, said she watched police put a man on the bus in Wawa on Sunday afternoon as it travelled west to Winnipeg.

Shortly after, she heard a commotion from the back of the bus and saw a man clutching his chest in pain. It's unclear if he was stabbed, but he was bleeding.

As Daher dialled 911, she said the man demanded to be let off the bus between Thunder Bay and Sault Ste. Marie. Police arrested him a short time later on the side of the Trans-Canada Highway.

David Roberts, from Manitouwadge, about 400 kilometres east of Thunder Bay, was charged with aggravated assault and two counts of breach of probation.

He faces a bail hearing today.