The report so far said he didn't shoot. He did however have a gun and was part of a criminal gang. Frankly, it was just an excuse for people to go steal televisions.
http://www.guardian.co.uk/uk/video/2011/aug/10/mark-duggan-handgun-ipcc-video As far as I am concerned, if you want to carry around an illegal firearm, you have to be prepared to face the consequences. He was armed. So no, he isn't innocent. If the police thought there was any chance of him firing, they were completely right to shoot.
Having seen some interviews with those involved, there were no real reasons given. Most just used the riots as an excuse to loot. Lock them up, and make them pay for the damage they have caused.