Chief Blair said that police feared the protesters would try to draw them away from the G20 security zone. That may explain why officers did not pursue the protesters on their smashing spree. Better to see some windows broken, they may have reasoned, than engage in running battles between police and protesters that scarred the face of Seattle during the world trade talks there in 1999.
The behaviour of the police, it has to be said, was not always impeccable.
They put on their biggest show of force at Queen's Park late in the day, using mounted police to clear the park around the legislature.
Some spectators said only a cursory, hard-to-hear warning was issued. At least one man was caught under horses' hooves and one woman journalist sustained a welt after a policeman hit her with a truncheon on the hip. Another journalist was hit by what appeared to be a bean-bag bullet, sometimes used for crown control. As the evening drew on, police beating on their riot shields and marching forward in stages cleared protesters and spectators from Queen's Park north - an area that was supposed to be a free protest zone. Chief has yet to explain adequately why that was necessary or justified.
By Sunday morning, nearly 500 people had been arrested, a shocking figure. It may prove that some of those detainees were arrested without cause in the aggressive police sweep that followed Saturday's vandalism.
But the ultimate blame for the weekend's events lies with the violent minority who spoiled what began as a peaceful, even festive protest, destroying property and frightening people in aid of - what?
"It doesn't do any good for any cause - and I don't even think they have one except causing violent acts," said a visibly angry Mayor David Miller. "It's sad for the city that these criminals chose to commit these criminal acts here."
Sad indeed. Toronto has seen scores of protests on any number of issues over the years but Mr. Miller said that this was the first time since a confrontation with anti-poverty protesters at Queen's Park more than a decade ago that we have seen one turn so violent - and this one was far worse. Only the so-called Yonge Street riot of 1992 comes close in recent history.
As Chief Blair confirmed, this was the only time police here have ever been forced to use tear gas in what is, for the most part, a remarkable safe and law-abiding city.
What was especially galling was the glee of the rioters as they made their merry way through the streets. Some of the group took cellphone photos or exchanged victory hugs. Other leapt up and down like madmen on the roofs of abandoned police cars and media vans.
When rioters set a police car on fire, a female protester said into her phone: "Let's get another car! They spent a billon dollars of our money on this. We might as well make them pay."
To call this a mob seems wrong. A mob is a fluid, changeable thing, with spontaneous moods that flare and die. This was much more organized and deliberate than that.
The whole thing had the feeling of a well-practiced game. Rioters knew just what to use to break shatter-proof windows. Some carried hammers and golf balls. Others pried bricks from the sidewalks or used the sticks from their protest banners and placards. Still others picked up folding metal sidewalk signs or newspaper boxes. They attacked the windows with a skill that seemed to come from experience or training.
Indeed, this was a well-organized "mob," with its own legal aides and marshals. There were even first-aid officers calling out "is anybody hurt?" with tender concern after every window shattered.
Fortunately, the chaotic day came to an end with no reports of serious injury. By Sunday morning, shopkeepers and businesses had already replaced many of the broken windows and some were covering their facades with plywood to prevent further damage today.
If the rampage showed how vulnerable big cities can be to this kind of deliberate action, it also showed how robust they are. Life goes on. Even on Saturday night, there was traffic on the streets and people on the sidewalks going about their business.
On Sunday morning, the subway started running again, the Eaton Centre planned to open as usual and things were getting back to normal. Outside of central downtown, most people were unaffected and learned about the events only through the media.
All the same, it hurt to see the city come to this - and for so little reason.