The lead police investigator for the 2011 Stanley Cup riots says the City of Vancouver's decision to allow throngs of young people to congregate and drink in the downtown core was a "recipe for disaster."

The Vancouver Police Department has previously said some of its recommendations in the lead-up to the June, 2011 Stanley Cup finals were ignored, but police have not criticized the city so directly before now.

Sergeant Dale Weidman with the Vancouver Police Department, speaking to an Ottawa security and intelligence conference Wednesday, prefaced his statement by noting he has to "keep some of my comments to myself because I still have to bring home a paycheque."

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But, he said, it was bad planning to let a volatile mix of factors come together in the streets surrounding the Cup final at Vancouver's Rogers Arena.

"Somebody in the city of Vancouver decided to, thought, it was a good idea to pack in 100,000-plus people in a confined area and allow them to have access to alcohol," Sgt. Weidman of the Vancouver Police Department told an Ottawa security conference Wednesday.

He boiled down the factors at play in the crowds behind the June 15 riots: "Young; alcohol; confined area," Sgt. Weidman said. "In my world, one plus one equals two."

"That's maybe," he said, "a recipe for disaster."

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Sgt. Weidman's comments were a blunt look at the challenges that have been facing police and the Crown as they react to pressure to bring charges against suspects in the riot, which caused millions of dollars in damage in downtown Vancouver and left 100 people injured.

The day after the riots, Vancouver Chief Constable Jim Chu laid blame for the mayhem at the feet of veteran scofflaws, fingering "criminals, anarchists and thugs who were bent on destruction and mayhem." Days later, he said his original assessment applied to the instigators of the chaos, but acknowledged rioters represented a wide spectrum of society.

Sgt. Weidman on Wednesday said the June 15 offenders were amateurs.

"There wasn't a so-called professional rioter element in this," he told the 2011 Canadian Association for Security and Intelligence Studies conference.

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"Unlike some other riots, this riot occurred because of alcohol, because of young males being jackasses," he said. "That's really what it came down to."

He noted, for instance, that rioters in some cases made poor efforts to disguise themselves. "One guy … he put his hat in front of his face," Sgt. Weidman said.

The police officer voiced the "tonne of pressure" he felt as the media and public questioned the speed with which authorities were laying charges. "Believe me, from my perspective, it got pretty tired pretty quickly … We had to gather evidence first."

Sgt. Weidman said police received 5,000 hours of video from security cameras and the public, adding it took a lot of time to properly document sources behind the clips.

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By comparison, he said, police after the 1994 Stanley Cup riots in Vancouver had only 100 hours of video to review.

"The majority of the public think that we can just charge people and throw them in jail," he said.

"I wish sometimes that was true, but unfortunately evidence is what puts people in jail, not just stories."

The officer said police have identified 313 separate "crime events" during the riots, some of which involved hundreds of people.

Sgt. Weidman acknowledged in response to an audience question that aggressive defence lawyers could probably thwart or slow convictions stemming from the riots by questioning evidence-gathering.

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"It's going to come down to money," the officer said.

"If I was a defence lawyer, this could be an opportunity to make a bit and so then you would attack it, the case, with [a focus on]continuity of evidence."

Added the officer: 'You could, if you were so inclined, could stretch this out to be quite a long trial per person."

He noted there is currently a year-long wait between when somebody is charged and when they go to trial in B.C.

"So this thing could be a long process."