G20 Protest in Toronto - Police stood by and did nothing while damage was being done. Part 2

Here is some video footage of what was being mentioned in the this post:
http://drivingtheporcelainbus.blogspot.com/2010/06/g20-protest-in-toronto-police-stood-by.html
There are 3 videos.
In part one, the vandals are in the background smashing windows, and you can see the police are standing a couple of blocks away on a side street not doing anything. And there are some other people milling around but not vandalizing, but watching the vandals.
In parts 2 and 3 you can see more police showing up on the side street and they eventually begin to head down an alleyway. Meanwhile, a lot of vandalism has been allowed to happen un-checked.

Video Part One
Video Part Two
Video Party Three

Why were there no police marching along beside the protesters or spread out along the route (which is normal practice in Toronto)? If they had done this, they would have been able to stop the vandalism on the spot and nab those responsible. Who convinced the police that they should abandon tried and true practices and be afraid of the peaceful protesters (thus allowing the few vandals free reign)? Why did the police then take revenge on the innocent peaceful protesters (because they missed their chance to stop and arrest the vandals) for the rest of the weekend by beating and arresting them?

UPDATE
And, there is this video from a photo journalist who actually followed the black block for 1.5 hours and said that there were no police around during their rampage of vandalism. They even smashed windows at the police station on College without being stopped! Curious.
G20 Toronto Black Block Get Green Light To Rampage?
(Thanks Fionna!)