GWEN IFILL: And we turn to the violent upheaval in Britain.
More than 500 rioters and looters have been arrested in four nights of unrest that has spread from London neighborhoods to other cities. The prime minister and other top officials interrupted summer vacations to deal with the violence.
We begin with this report from Keir Simmons of Independent Television News.
KEIR SIMMONS: The worst riots for a generation left buildings still burning today. This was an electronics warehouse in Enfield, North London. South of the city, this was a furniture store in Croydon. It withstood two world wars, but was razed to the ground in one night. Across London are broken shops and lives.
WOMAN: I don't know why people -- oh, my God. I don't know why people do this.
KEIR SIMMONS: Overnight, there were 20,000 999 calls, more than 100 officers injured.
After an emergency meeting in Downing Street, the prime minister promised tough action.
DAVID CAMERON, British prime minister: I have this very clear message to those people who are responsible for this wrongdoing and criminality: You will feel the full force of the law. And if you are old enough to commit these crimes, you are old enough to face the punishments.
KEIR SIMMONS: As he visited south London, it was announced Parliament will be recalled on Thursday.
But it is all too late, say some, who heckled his home secretary and London's mayor.
BORIS JOHNSON, mayor of London: I know there are questions about the police response and about police numbers. And we are certainly...I understand. And we are certainly -- and we are certainly...
KEIR SIMMONS: Whilst, in Birmingham, where there was further violence overnight, the deputy prime minister was booed.
KEIR SIMMONS: And there are further questions tonight about the shooting of Mark Duggan, which sparked the first riots. Ballistic test results revealed no evidence that he opened fire at police officers before he was shot dead.
But the violence that followed has now left a 60-year-old man from Ealing suffering life-threatening injuries. And the 26-year-old was shot in South London, though it's not clear if his death was related to the disturbances.
The operation to prevent those riots running into a fourth night now involves 16,000 officers. And there have been calls for tougher action, like the use of baton rounds or a water cannon, though such moves would be controversial.
SIR HUGH ORDE, Association of Chief Police Officers: My current judgment is water cannon is entirely inappropriate for policing in the capital. And those who keep making comments about it clearly do not know what they're talking about. You use water cannon in fixed locations to deal with large crowds to buy distance, likewise with baton rounds. That having been said, I know the commissioner will continue to review his tactics.
KEIR SIMMONS: Still, as shop owners prepared for the worst, with shutters down, the police said they are employing new tactics aimed at stopping another night of violence.