LONDON - In the battle to bring calm to the British streets, authorities are playing both sides of technology - employing facial recognition software to hunt suspects while at the same time considering restrictions on social media the government claims has been used as an organizing tool for rioters.
Officers are feeding photographs of suspects through Scotland Yard's newly updated face-matching program, which has been under consideration for London's 2012 Games.
A law enforcement official, who spoke to the Associated Press on condition of anonymity, said that facial recognition is one of many tools police are using to hunt suspects still at large. Other techniques include posting headshots to photo-sharing site Flickr and old-fashioned public appeals.
A spokesman for Scotland Yard confirmed Thursday that facial recognition technology was at his force's disposal.
Meanwhile, Prime Minister David Cameron said the government, police and intelligence services were looking at whether there should be limits on the use of social media sites like Twitter and Facebook or services like BlackBerry Messenger to spread disorder.
Government officials said they were discussing with spy agencies and communications companies whether messaging services could be disabled in specific areas, or at specific times.
Authorities are considering "whether it would be right to stop people communicating via these websites and services when we know they are plotting violence, disorder and criminality," Cameron said.
"Police were facing a new circumstance where rioters were using the BlackBerry Messenger service, a closed network," to organize riots, he said. "We've got to examine that and work out how to get ahead of them."
Cameron promised vigorous and wide-ranging measures to restore order and prevent riots erupting again on Britain's streets including also taking gang-fighting tips from American cities.
Cameron told lawmakers there would be no "culture of fear" on Britain's streets, as police raided houses to round up more suspects from four days of rioting and looting in London and other English cities. He said the government was "acting decisively" to restore order after the riots, which shocked the country and the world.
Cameron said authorities were considering other new powers, including allowing police to order thugs to remove masks or hoods and evicting troublemakers from subsidized.
"We will not allow a culture of fear to exist on our streets," Cameron said. "We will not let a violent few beat us."
Lawmakers were summoned back from their summer vacations for an emergency session of Parliament in the riots as government and police worked to regain control, both on the streets and in the court of public opinion. Calm prevailed in London overnight, with a highly visible police presence watching over the capital, but tensions remained high across the country.
Cameron promised tough measures to stop further violence and said "nothing should be off the table," including water cannons and plastic bullets.
He said riot-hit businesses would receive help to get back on their feet, and promised to look to the United States for help in fighting the street gangs he blamed for helping spark Britain's riots.
Cameron told lawmakers that he would look to cities like Boston for inspiration, and mentioned former Los Angeles and New York Police Chief Bill Bratton as a person who could help offer advice.
He said he wanted to look at cities including Boston and Glasgow that had fought gangs "by engaging the police, the voluntary sector and local government."
"I also believe we should be looking beyond our shores to learn the lessons from others who have faced similar problems," Cameron said.
Cameron said that, in the future, police would be able to order people to remove masks, hoods or other face coverings when they suspect them of concealing their identity to carry out a crime. Currently, officers must seek approval from a senior officer.
A program that can ban gang members from meeting together, loitering in certain places, or displaying gang insignia will also be extended, he said.
Meanwhile the number of people arrested in London rose to 922 since trouble began on Saturday, with 401 suspects charged.
The huge number drew notice. Peter Tapsell, a veteran Conservative Party lawmaker, called on Cameron to draw inspiration from the response of U.S. authorities to anti-Vietnam protests in the 1970s.
Tapsell said he recalled law enforcement in Washington, D.C., rounding up demonstrators and imprisoning them in a sports stadium. He did not elaborate, but authorities in 1971 set up an emergency detention center next to Washington's RFK stadium to hold demonstrators after the largest mass arrest in U.S. history.
Tapsell asked Cameron if Britain's Wembley Stadium, the country's showpiece soccer arena could be used. Cameron insisted the stadium would be used only for "great sporting events," not the detention of rioters.
Deputy Assistant Commissioner Stephen Kavanagh said raids to round up suspects began overnight, and more than 100 warrants would be executed. Hugh Orde, head of the Association of Chief Police Officers, said there would be "hundreds more people in custody" by the end of the day.
London was largely calm overnight, with thousands of extra officers on the streets. The London force said it would keep up the huge operation involving 16,000 officers for at least one more night.
There was a brief outbreak of trouble in Eltham, southeast London, where a group of largely white and middle-aged men who claimed to be defending their neighborhood pelted police with rocks and bottles. Police said the incident had been "dealt with" and a group was dispersed.
Other cities where looters had rampaged earlier this week also came through the night largely unscathed, though for the first time minor disturbances were reported in Wales.
Tensions flared in Birmingham, where a murder probe was opened after three men were killed in a hit-and-run incident as they took to the streets to defend shops from looting.
Chris Sims, chief constable of West Midlands Police, said a man had been arrested on suspicion of murder. Police on Thursday were given more time to question him.
Overnight, a deployment of 1,000 police and heavy rains discouraged rioters from taking to the streets for a third night. A courthouse stayed open all night to prosecute 26 people accused of burglary, arson and riotous behavior.
Police said they had arrested 330 people over the past four nights, including a 14-year-old girl who was brought to a police station by an uncle who suspected her of wearing stolen clothes.
Scenes of ransacked stores, torched cars and blackened buildings have frightened and outraged Britons just a year before their country is to host next summer's Olympic Games, bringing demands for a tougher response from law enforcement and calls for the government to scrap plans to cut police budgets.
Cameron's Conservative-led government is slashing 80 billion pounds ($130 billion) from public spending by 2015 to reduce the country's swollen budget deficit measures that include cuts to police budgets. A report last month said the cuts will mean 16,000 fewer police officers by 2015.
Cameron said the cuts would not hit front-line officers.
He said that "at the end of this process of making sure our police budgets are affordable we will still be able to surge as many police officers on to the streets as we have in recent days."
Soccer authorities announced Thursday that Tottenham Hotspur's season-opening match against Everton on Saturday was being postponed following Saturday's disorder in the Tottenham neighborhood, which sparked trouble across England.
Officials said there were ongoing safety concerns in the area around the north London club's White Hart Lane stadium, which has seen police resources stretched.
A Wednesday match between England and the Netherlands at London's Wembley stadium also was canceled.
Britain's riots began Saturday when an initially peaceful protest over a police shooting turned violent. That clash has morphed into general lawlessness that police struggled to halt.
While the rioters have run off with goods every teen wants new sneakers, bikes, electronics and leather goods they also have torched stores apparently just to see something burn. They were left virtually unchallenged in several neighborhoods, and when police did arrive they often were able to flee quickly and regroup.
There were chaotic scenes Thursday at courthouses, several of which sat through the night to process scores of alleged looters and vandals, including an 11-year-old boy.
The defendants included Natasha Reid, a 24-year-old university graduate who admitted stealing a TV from a looted electronics store in north London. Her lawyer said she had turned herself in because she could not sleep because of guilt.
Also due to appear in court were several people charged with using Twitter and Facebook to incite violence.