Shortly after accused U.S. rioter Kevin Chianella flew to Toronto's Pearson Airport earlier this month and surrendered to police, he learned of the huge database – tens of thousands of images and video clips – that had been assembled.

Mr. Chianella, 20, of New York, is facing 53 criminal charges, including arson, arising from the June, 2010, weekend when foes of the G20 summit burned four police cars, smashed dozens of windows, ran amok through the city core – causing $2.5-million in damage – and set the stage for the biggest mass arrest in Canadian history.

Greeting him at the 23 Division station the evening of his surrender was Detective Sergeant Gary Giroux, seconded from the homicide squad to lead the identification and roundup of the protesters on his hit list, many of whom had been masked.

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"So there's hundreds and hundreds of photographs of Chianella," Det. Sgt. Giroux recounted. "And when I showed maybe 50 of them to him and said, 'This is less than 1 per cent of the photographs we have of you,' he seemed a little stunned by that, a little overwhelmed."

Mr. Chianella is one of five young Americans charged with summit-related offences, and the way the five were laboriously tracked down underscores the growing role of cameras in law enforcement. One suspect has an extradition hearing scheduled for Wednesday.

The mass arrests that drew accusations of police heavy-handedness occurred on the summit's second day – Sunday, June 27. More than 1,100 largely peaceful demonstrators and onlookers were scooped up and held in a makeshift detention centre; most were released within hours. In all, 317 people were charged, chiefly with minor offences, and all but a couple of dozen were eventually acquitted.

But they were not the focus of the 27-member police team created on the Monday morning. Its task was to find the people who had wreaked havoc on the Saturday of the weekend summit. Its final target list comprised 47 people, average age 27, charged mostly with mischief but also with arson, assault, theft and using a disguise.

Nearly three years later, 90 per cent of that group have been convicted – most escaped jail time beyond spells of pretrial custody – and the reeling-in is nearly complete.

Just seven of the 47 remain before the courts – two Canadians and the five Americans. Mr. Chianella, youngest of the five, faces the most charges, including arson, assaulting police with a weapon, and multiple counts of mischief endangering life.

He was not the first to waive extradition and fly to Toronto. Shortly before, 25-year-old Boston architect Quinn McCormic surrendered the same way; so, too, has Richard Morano, 22, of Pennsylvania. All three were granted bail and returned home pending court appearances.

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That leaves Joel Bitar, another New Yorker, 26, under house arrest with an extradition hearing set for Wednesday; and Dane Rossman, 25, jailed in Florence, Ariz.

So what linked these five players, aside from an alleged willingness to help smash up a foreign city? The short answer looks to be: not much.

Interview requests sent to the accused and their supporters went unanswered, and there are no clues in a criminal-records check. Of the five, only Mr. Rossman had had a previous run-in with the law, for minor, unpolitical offences. And while Det. Sgt. Giroux lists some of the riot gear the five allegedly brought to Toronto – masks, goggles, gloves, elbow pads – he sees no evidence they were part of any presummit plot. "Geographically, it would suggest they were not," he said.

Canadian activist and accused ringleader Amanda Hiscocks, who did prison time for her role in the G20 protests, says she knows of the Americans only from press reports. "I don't get the sense that the people that I know here know them, or did know them before, I'm pretty sure not," she said.

The rioting that Saturday had two main venues: the intersection at Queen Street and Spadina Avenue, a relatively easy part of the investigation because most of the participants there were unmasked; and the corner of King and Bay Streets, where hundreds of "black bloc" demonstrators converged.

At both spots were undercover officers with cameras, while overhead flew helicopters and even airplanes; in all, they shot close to 10,000 frames. Over the next few weeks, more material arrived – discs and memory sticks dropped off by private citizens, video from store cameras – until the data base comprised more than 80,000 items.

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Then commenced an elaborate mix-and-match exercise.

Black bloc tactics entail looking as anonymous as possible, in masks and dark clothing, to thwart identification. So once the police had spotted a window-smasher, or car-burner, the person was followed. "What they would often do was gather in groups and face inward," Det. Sgt. Giroux said. "The people inside the ring disrobed, leaving their clothes on the ground and then merging into the crowd."

All the time the cameras kept clicking, helping build detailed files on individuals – matching a masked rioter to a pair of distinctive boots, for example, or to a conspicuous body type. Mr. Bitar, for instance, was easy to follow because he is so tall.

Other suspects were identified by more traditional means: witness reports; information from other suspects; checks with police agencies. And some of the accused had been arrested earlier on lesser charges.

The five Americans were left to last in the roundup. With their names and hometowns established, a request to the U.S. Marshal's Service was relayed, via the FBI office in Toronto, and after surveillance they were arrested.

"Every one of these prosecutions will be identity-based," Det. Sgt. Giroux said. "So if we can prove that the individual who's masked is the individual sitting in court, they'll be convicted."