Elizabeth McQueen was driving on the Cambie Street Bridge Wednesday when she saw that a distraught, shirtless man was crossing traffic lanes and jumping barriers as police pursued him.

"My first thought is, 'This could go very wrong, very quickly.' So that's why I grabbed my phone and I started filming it," she told CBC News.

What she captured on her camera's video recorder sickened her and left her with serious questions about how police deal with agitated individuals.

The video shows the man walking backwards, with his hands up, as police advance. The man is then tackled, with five officers piling on top of him. One officer appears to start punching.

"There's five people sitting on top of him, holding him down. Why are you punching?" McQueen asks, reviewing the footage.

"If this guy is having a mental health issue, he needs help. He doesn't need to have the crap beat out of him," she says.

Vancouver Police Department spokesman Const. Brian Montague said the man had been in the police station at the south end of the bridge moments before and began following an off-duty officer across the bridge. When the man threw a knapsack over the side of the bridge and started taking off his clothes, the officer called 911.

Cambie Street Bridge police takedown video still

Vancouver Police Department spokesman Const. Brian Montague said a man that officers apprehended on the Cambie Street Bridge not only appeared agitated but may have been on drugs. He said police had to act fast to prevent the man from harming himself or someone else. (Elizabeth McQueen)

Montague says the man not only appeared agitated but may have been on drugs. He said police had to act fast to prevent the man from harming himself or someone else.

"Decisions have to be made quickly and a decision to take him into custody was done," he said.

Montague said the concrete barrier obscures the view showing where the punches were landing, and may also obscure reasons why force was being used.

"It doesn't show everything that is occurring. Only an investigation into the entire incident can really decide whether or not the actions of our officers were justified."

But McQueen says the apparent punching "was completely over the top," and she wants to know why it was deemed necessary.

Dave Jones, a former police officer now working as a security consultant agrees that police have a responsibility to look into the incident.

"I think the public, seeing that, you have a right to say, 'what was happening? Why? Was it an appropriate use of force?'" he said. "I think the police department is under an obligation to answer those questions."

The VPD says its Professional Standards Section (PSS) has the recording and is looking at it, but has not decided whether or not to open an investigation into the officers' actions. The PSS could launch an investigation on its own, or wait until there is a formal complaint made by the man in the video, or by a member of the public.

With files from the CBC's Kirk Williams