Manchester could have been spared the August riots if police in London had acted sooner, according to the city's chief constable.
Greater Manchester Police chief Peter Fahy told BBC Panorama that copycat violence broke out after people saw rioters were "getting away with" their behaviour in the capital.
Mr Fahy said: "A certain group of people saw what was happening in London and decided they seemed to be getting away with it. The authorities weren't in control and they decided they wanted their opportunity."
He told the programme he did not regret the decision to send 100 officers from Greater Manchester Police to help deal with the situation in London.
"We knew what was absolutely critical was that there needed to be control of London. Because that was just creating more and more copycat violence up here."
Mr Fahy added: "I think you'd have to say with hindsight if London had been under control sooner we probably would not have faced the problems in Manchester."
Manchester Police have arrested more than 350 people in connection with the riots. Mr Fahy told the programme the force is still tracking down hundreds of suspects from at least 300 crime scenes.
Early findings from the Metropolitan Police's review into its policing of the riots concluded that too few officers were deployed on the first night of violence.
The disturbances began in Tottenham, north London, on Saturday August 6 in response to the fatal police shooting of father-of-four Mark Duggan, 29, and spread throughout the capital and then across England.
Scotland Yard said it had about 3,000 policemen and women on duty across London on the first night of the riots, and it deployed 480 trained public order officers to the disorder in Tottenham. By Monday August 8, by far the worst night of violence in the capital, there were around 6,000 officers on duty, of whom 1,900 had specialist public order training.
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