A local psychiatrist says the passengers from the Greyhound bus where one passenger murdered another will have to undergo counseling.

Dr. Jitender Sareen told CTV News the people who saw the violence will likely have severe trauma.

"People who have gone through this kind of a severe traumatic event will have distress will have a lot of fear anxiety often have nightmares and flashbacks of the actual incident," he told CTV News. "A lot of those people will actually have a resolution of those symptoms and those symptoms will go away over the next few weeks."

Several of the passengers who saw the attack on the bus say they became physically ill at the time it happened. They also say they have been having trouble sleeping.