MONTREAL -- After city leaders said Monday that they'd ensure an independent review into a violent incident at a metro station this weekend, Montreal's transit agency has clarified what that will be.

The STM has already done a preliminary investigation, the agency wrote in a statement. Now a lawyer, Marco Gaggino, has been asked to audit those preliminary findings.

The STM has found, so far, that transit officers followed their use-of-force training in an incident caught on video where two of them pinned a woman to the ground, after she fare-dodged and tried to leave the scene, and one officer appears to be punching her in the head.

The agency said that during the altercation, the woman bit the officer hard enough to break the skin. Her friends told CTV she needed a hospital visit after the incident. She hasn't yet spoken to media.

"The preliminary findings of the internal investigation, including a study of the various videotapes available, indicate that the intervention of the inspectors followed the rules for the use of force taught at the Quebec National Police Academy," the STM board wrote in a statement.

"The STM asked Mr. Gaggino to audit the analysis and is open to welcoming and implementing any recommendations that may result from it."

The STM described Gaggino as a "lawyer specializing in police ethics" in its release, dated Tuesday, and said he will provide independent oversight.

Documents available online show that Gaggino has previously represented Quebec police on several occasions, including acting for the Quebec Mounted Police Members’ Association in a labour matter and for a provincial police group called the ADPQ when it wanted participant status in the Viens Commission looking into Indigenous experiences in Quebec.

Gaggino hasn't yet responded to a request for comment about his training in police ethics or how he plans to approach the audit.

The STM says it isn't commenting further on the process right now and hasn't given a timeline for when the audit will be done.

A spokesperson for the City of Montreal said the decision to hire Gaggino was what it had in mind, though it wasn't its own choice.

"It is a decision of the STM's Board of Directors that meets our orientations and our expectations, namely to have a more neutral process while waiting for the [provincial police watchdog agency] to have jurisdiction," said spokesperson Catherine Cadotte.

She was referring to the fact that Montreal transit inspectors will get a new, more official "constable" status in July that will both give them more powers and subject them to more oversight.

Like regular Quebec police, their actions can be investigated by the Police Ethics Committee and by the BEI, the watchdog agency, which automatically investigates when anyone is hurt or killed in connection with police actions.

The STM's board said in its statement that it knows the footage shot this weekend has circulated widely and has been a blow to people's trust in the transit system.

"I recognize that what happened may seem shocking," said Philippe Schnobb, chairman of the STM's board, according to the statement.

"We read, listen and see what is said and posted and know that the relationship between us and our customers has been shaken by the content of the video."

As a public transit agency, maintaining the trust of customers "is essential, which is why we're calling on an independent external expert," he said.

While the board said that so far, it seems the officers didn't step outside their training, the general manager of the transit network said he wants to look into how to avoid such incidents from now on.

“Our inspectors have a complex job," said Luc Tremblay, the general manager. "I want us to look at what led to this intervention and what could be done to reduce the need for this type of approach in the future."

The statement also said that the change to special constable status in July will also bring an improvement in transit officers' training.