"I don't think there is another city in the U.S. that has as an extensive and integrated camera network as Chicago has," said Michael Chertoff, the former Homeland Security secretary, told the Associated Press.
The city has linked thousands of cameras- from street poles to skyscrapers and the transit system- in a network that spans across most of Chicago. Officials can watch video live at a sprawling emergency command center, police stations and even some squad cars.
Those cameras allow detectives to piece together information in crimes, including the death of Chicago's school board president. Michael Scott was found shot to death in a river last fall and cameras helped prove it was a suicide.
Within days, police recreated Scott's 20-minute drive through the city using high-tech equipment that singled out his car on a succession of surveillance cameras, handing the image from camera to camera. The video didn't capture Scott's final moments, but it helped convince police his death was a suicide: He wasn't followed. He wasn't following anyone. He never picked up a passenger.
The investigation offered a riveting demonstration of the most extensive and sophisticated video surveillance system in the United States, and one that is transforming what it means to be in public in Chicago.
Chicago's camera system compared to other big cities
New York has plenty of cameras, but about half of the 4,300 installed along the city's subways don't work. Other cities haven't been able to link networks like Chicago. Baltimore, for example, doesn't integrate school cameras with its emergency system and it can't immediately send 911 dispatchers video from the camera nearest to a call like Chicago can.
Even London -- widely considered the world's most closely watched city with an estimated 500,000 cameras -- doesn't incorporate private cameras in its system as Chicago does.
Big Brother is watching
While critics decry the network as the biggest of Big Brother invasions of privacy, most Chicago residents accept them as a fact of life in a city that has always had a powerful local government and police force.
And authorities say the system helps them respond to emergencies in a way never before possible. A dispatcher can tell those racing to the scene how big a fire is or what a gunman looks like. If a package is left sitting next to a building for more than a few minutes, a camera can send an alert.
Cameras have recorded drug deals, bike thefts and a holiday bell ringer dipping his hand into a pot outside a downtown store. Footage from a camera on a city bus helped convince a suspected gang member to plead guilty to shooting a 16-year-old high school student in 2007.
In the death of the school board president, the cameras helped diffuse mounting suspicion and anger.
"It really closed that piece of the puzzle," police Superintendent Jody Weis said. "We don't know what was going through his head, but we definitely know he was alone."
About the network
The network began less than a decade ago with a dozen cameras installed in Grant Park to deter violence during the annual Taste of Chicago festival. It now includes private cameras as well as those installed by a variety of public agencies.
While authorities won't say exactly how many cameras are included, with 1,500 installed by emergency officials, 6,500 in city schools and many more at public and private facilities, nobody disputes an estimate of 10,000 and growing. Weis said he would like to add "covert" cameras, perhaps as small as matchboxes.
City officials from around the world have visited Chicago to see the system and how effective it is.
Chicago police point to 4,000 arrests made since 2006 with the help of cameras. And, an unpublished study by the Washington-based Urban Institute found crime in one neighborhood -- including drug sales, robberies and weapons offenses -- decreased significantly after cameras were installed, said Nancy La Vigne, director of the institute's Justice Policy Center.
"It does stop people from coming out and acting the fool," observed Larry Scott, who lives in one of the city's last remaining public housing high rises.
He said residents rarely complain, unless they get caught for a minor offense or the cameras fail to record a violent attack.
"People were upset when that boy was killed by the 2-by-4 and there were no pictures," he said, referring to the beating death of a high school student that was recorded by cell phone but not city cameras last year.
Police say they usually hear from Chicago residents about the cameras only when they want one installed in their neighborhood or worry one will be removed. Such a claim is supported by an unlikely source: The American Civil Liberties Union, which has criticized the use of cameras as an invasion of privacy and ineffective crime fighting tool.
"It does appear that people only object is when they get a ticket (because of a camera) for running a red light," ACLU spokesman Edwin Yohnka said.
Although courts have generally found surveillance cameras placed in public don't violate individuals' privacy, Yohnka said they could too easily be misused.
"What protections are in place to stop a rogue officer from taking a highly powerful camera and aim it in a way to find or track someone who is perhaps a former love interest or something like that?" he asked.
Aric Roush, director of information services at the city's 911 center, responded that dispatchers see nothing officers wouldn't see if they were on the scene.
"You can't afford to put a police officer on every single corner (and) it is a lot more cost effective and efficient to put a camera where you don't have eyes," he said.
Chicago residents tend to be tough on crime and are likely to support any tool police use, said Paul Green, a Roosevelt University political science professor. Many literally applauded the officers who swung billy clubs at protesters during the 1968 Democratic National Convention, he recalled.
Mayor Richard Daley, he said, "could put 10,000 more cameras up and nobody would say anything."
The Associated Press contributed to this report.