It appears a known criminal (gangs, drug-dealing) with a loaded handgun was shot by police while resisting arrest; he may or may not have shot a police officer [first] at the time of his arrest ...
So if it's not gangs trying to violent show their power then what is the motivation in your opinion? Why sudden anger towards the police _from the general populus_?
FWIW the buzz appears to be "send in the troops" rather than this being in any way justified demonstration (like maybe G8 demonstrations).
http://www.independent.co.uk/news/uk/crime/a-dead-man-a-cruc...
http://www.telegraph.co.uk/news/uknews/law-and-order/8687403...
http://www.guardian.co.uk/uk/2011/aug/08/mark-duggan-profile...