A witness to Monday's altercation at de la Savane metro station has told CBC that he saw a public transit agent leave her kiosk and assault a passenger.

Jamie Salomon witnessed the event and confirmed the story of Mina Barak, who alleges she was punched and told to go, "back to [her] country" after a disagreement with an STM agent.

Salomon said he was coming out of the metro station a few minutes before 1 p.m. when he saw an agent come out of her kiosk, slam the door and start "pounding" Barak. He started to call 911, but then hung up to go over and try to stop the confrontation.

"It was really crazy, de la Savane is a very quiet Metro station ... It was really bizarre, really insane, really horrifying," he said.

According to Barak, the situation started with a faulty metro ticket machine. She attempted to buy two tickets at the de la Savane metro station, but the machine was out of order and took her money.

She said she turned to the clerk in the ticket booth to explain, in English, what had happened. According to Barak, the STM employee refused to serve her in English, and emerged from booth, put her in a headlock and started to punch her repeatedly.

The struggle went on for about a minute, according to the witness. He tried banging on the booth and screaming to draw as much attention as possible, hoping that would help stop the altercation.

"I had no idea what they were fighting about," Salomon said, explaining that he initially thought the agent was upset over a personal insult. "She was just enraged," he added.

According to Salomon, it seemed that Barak was surprised by the alleged assault. Salomon is concerned about what would have happened if someone hadn't stepped in.

"Finally this young man pulled Mina Barak out of the way, out of the clutches of the agent," he said.

STM launches investigation

Montreal's public transit commission announced yesterday it will be launching an internal investigation into the incident.

The vice-chair of the STM, Marvin Rotrand, said a complaint has been filed with police.

"Like any human institution with thousands of thousands of employees, you are always going to have a couple of people ... who have a chip on their shoulder or otherwise discredit everyone else," Rotrand said.

Montreal police said they're reviewing surveillance tapes of the incident.

According to Rotrand, the STM agent received treatment at a hospital.

Salomon said he was surprised to hear that, adding that she didn't seem injured after the altercation.

Going forward, Rotrand said the STM will review its security tapes and offer any help it can to the police department.

Montreal police and the STM have refused further comment.