CHICAGO  At first glance, Chicago’s latest crime-fighting strategy seems to be plucked from a Hollywood screenplay. Someone sees a thief dipping into a Salvation Army kettle in a crowd of shoppers on State Street and dials 911 from a cellphone. Within seconds, a video image of the caller’s location is beamed onto a dispatcher’s computer screen. An officer arrives and by police radio is directed to the suspect, whose description and precise location are conveyed by the dispatcher watching the video, leading to a quick arrest.

That chain of events actually happened in the Loop in December, said Ray Orozco, the executive director of the Chicago Office of Emergency Management and Communications.

“We can now immediately take a look at the crime scene if the 911 caller is in a location within 150 feet of one of our surveillance cameras, even before the first responders arrive,” Mr. Orozco said.

The technology, a computer-aided dispatch system, was paid for with a $6 million grant from the Department of Homeland Security. It has been in use since a trial run in December. “One of the best tools any big city can have is visual indicators like cameras, which can help save lives,” Mr. Orozco said.