An activist wearing black clothing breaks a window with a chair in Toronto's financial district during a protest against the G20 summit on Saturday. (Darren Calabrese/Canadian Press)

When police launched a raid Sunday at the University of Toronto, the items they seized included materials that have become symbolic of the G20 summit's violent underbelly: black clothing.

The Integrated Security Unit said officers found "street-type weaponry," including bricks, while officers who were combing through bushes and garbage cans found items of black clothing.

Activists set this police car on fire amid a protest that wound through the streets of downtown Toronto on Saturday. (Nathan Denette/Canadian Press)

Black clothes — hoodies, masks, bandanas and anything else that disguise an identity — were easily seen Saturday as a march through Toronto's downtown core took increasingly ugly turns.

The so-called Black Bloc tactic has been used at other international summits, as well as at this February's Olympics in British Columbia. Under the tactic, activists who sympathize with anarchist or anti-capitalist causes use black clothing to disguise themselves while they vandalize property or confront authorities, only to slip quickly out of the clothing later while they blend into crowds.

While the use of the Black Bloc tactic had been anticipated, Toronto police Chief Bill Blair said its perpetrators would not be tolerated.

"They deliberately provoke violent confrontation to draw the naive and curious into their mob mentality," Blair told reporters Saturday.

"They use the numbers of a mob to avoid detection. We saw this tactic — often called a Black Bloc tactic — demonstrated in all its mindless violence and destruction," Blair said.

"I want to assure you that the persons responsible will be held accountable. We know many of the members of these groups. Over the past several days we have apprehended many of their leaders."

Symbols of capitalism targeted

As in the past, Black Bloc supporters targeted symbols of capitalism, from banks to multinational franchises like Starbucks.

Scores of arrests that began Saturday continued Sunday, with activists arrested at the University of Toronto. Most of those arrested are not believed to be students at the university and many are reported to have come to Toronto from Montreal.

CBC News reporter Muhammad Lila, though, noted that activists who were arrested at U of T made no effort to disguise their faces, unlike Black Bloc activists who made numerous efforts on Saturday to avoid being photographed or recorded on video, even when they were masked.

"The people [who] are being arrested today are not hiding their faces at all. In fact, they're turning to the cameras and saying, 'Listen, guys, we're innocent. We're here just to protest peacefully,'" Lila said Sunday.

Lila said, however, that the discovery of numerous pieces of black clothing is suspicious.

"It's not unusual to find discarded clothing here and there around the downtown core of Toronto," Lila said.

"But to find several items of black clothing, all in a very close proximity, all literally just steps away from where they conducted this raid — that certainly could turn out to be a telling detail and a very key piece of evidence."

Black Bloc activists did not endear themselves to the thousands of others who marched peacefully Saturday, nor to authorities. Toronto Mayor David Miller said he could only call them "thugs," and said their destruction distracted public attention from issues that are worthy of debate.

"People are calling them protesters. That is not fair to the people who came to protest," he told CBC News on Saturday.

Those who have studied the Black Bloc tactic say confrontation with police is not only expected, but encouraged.

"It's more of a philosophy or an approach, or actually I suppose the most accurate term is an extreme sport," said John Thompson, who works with the Mackenzie Institute think tank in Toronto.

Reaction was scathing in social media networks. A heavily retweeted message on Twitter, sent Saturday through the @lifeonqueen account, took aim at the hypocrisy of masked anarchists: "Nothing says 'courage of yr convictions' lk a mask & changing clothes after committing acts of arson & vandalism."

- With files from The Canadian Press