A criminal charge placed against a police officer who is alleged to have assaulted a demonstrator during the G20 Summit in downtown Toronto came as a result of the public standing up for itself, one civil liberties expert said.

Graeme Norton, of the Canadian Civil Liberties Association, said it is unlikely anything would have come from the incident if other demonstrators had not been there to video tape the arrest of Adam Nobody on June 26.

"From what we have seen it doesn't seem that it would have (led to charges)," Norton told CTV Canada AM on Wednesday.

On Tuesday, Ontario's Special Investigations Unit announced that a Toronto police office had been charged with assault with a weapon, following the review of video tape of Nobody's arrest made available on YouTube.

The arms-length agency had originally ruled that while Nobody appeared to have been roughed up, it was impossible to identify the perpetrator. The charge came after more evidence was presented to the SIU.

"It was only after the public came forward with additional information in the form of video tape and photographic evidence that we have now seen charges being laid," Norton said.

The arrest came after an extended investigation that had originally been closed without any charges being laid.

In the YouTube video shot of the incident, Nobody is seen being swarmed and at least one officer can be seen making a punching motion. Nobody had to be treated for a fracture below his right eye.

Toronto Police Chief Bill Blair asserted in a Nov. 29 interview that the video had been significantly tampered with.

"He said that the police were arresting a violent armed offender and that a segment depicting the use of a weapon had been removed from the tape," the SIU said.

John Bridge, who shot the video, said there was a gap because he turned his camera off for a few seconds, and then turned it back on when he saw Nobody being arrested.

He supplied the SIU with his original video, which was of higher quality than the YouTube version.

Blair issued a statement on Dec. 3 that said he had no evidence of any attempt to mislead with the original video -- and no evidence Nobody was armed.

On Dec. 9, the SIU received new video from the Toronto Star. A member of the public also provided a third video, and the Toronto Police Service gave the SIU a list of 15 officers who may have been in the area where Nobody was taken down.

The SIU designated 12 of the 15 officers as witnesses and three as subject officers, meaning they were under investigation.

"The twelve officers who were interviewed were shown the Bridge video of the incident and stills taken from other videos," police said.

"None of the twelve witness officers who were said to be in the vicinity of and/or involved in the arrest of Mr. Nobody were able to positively identify themselves as being depicted in the videos, nor could they identify the other involved officers."

The subject officers declined to give statements, which the SIU noted is their right.

Toronto Police Service also gave the SIU the name of another witness officer. He identified one of the subject officers.

Const. Babak Andalib-Goortani has been charged with assault with a weapon. He is scheduled to appear in court on Jan. 24.

Nobody made a second complaint about being taken away and beaten by two plainclothes officers after his initial arrest. The SIU said it has further investigated that allegation and hasn't found enough corroborative evidence to warrant the laying of a charge.

In November, the SIU closed five other investigations stemming from the summit without laying charges. In four of the cases, the SIU said there was no evidence the protesters suffered injuries at the hands of police. In the fifth case, the complainant could not identify his attacker because his eyes were closed.

During the summit, Police arrested more than 1,000 people. About 300 were actually charged with criminal offences, but a large proportion of those have been stayed.

Protesters gathered in Toronto in the days before the two-day summit of leaders from the world's 20 largest economies.

The biggest protest took place on June 26, a Saturday. A small group broke from a peaceful main crowd. Using so-called Black Bloc tactics, they went on a 90-minute vandalism rampage. Business storefronts were shattered and police cruisers burned.

In response, police carried out a widespread crackdown to restore order. The area around Queen's Park was to be a designated protest zone, but the Nobody incident occurred there.

On Wednesday, Norton said the Canadian Civil Liberties Association is requesting a public inquiry be held into policing at the G20.

"There is certainly no question that it is a difficult task to police an event of this nature. That said, in our view some of the arrests, if not many of the arrests, were unwarranted and unnecessary," Norton said.

"In our view this is the reason that there should be a full-blown public inquiry into the actions and events of the G20. We want to see the issues probed further. We want to see an examination of how policing action was carried out. And we'd like to see recommendations and changes made to how these events are policed in the future."

Steven Skurka, CTV's legal analyst, said there has already been a report from Ontario's ombudsman and there are two more reports pending from two senior judges.

"At the end of the day if there is still and unsettling feeling that we don't have proper accountability, there may be a need for a public inquiry," Skurka told CTV's Canada AM.

"I still think people believe in their police force, but I think they take a more skeptical eye about it."