The cops -- at least the good ones, who are presumably the majority -- have as much reason to want these recordings as the accused. The best defense against a phony charge of police brutality is a video showing exactly what the officer said and did. A suspect who is visibly inebriated or violent will have a hard time refuting the camera's testimony in court.

Yet Chicago has dragged its feet, and it's not alone. After the 1991 Rodney King beating, a commission recommended that the Los Angeles Police Department mount cameras in its squad cars. It installed some but soon got rid of them.

A federal monitor proposed the idea again in 2005, but the police chief, The Los Angeles Times reported, "said he saw it as a long-term project." Last year -- 17 years later -- the LAPD finally decided to equip some vehicles.

Contrast that with Chicago Mayor Richard Daley's enthusiasm for other types of video. Chicago now has some 2,250 surveillance cameras to detect criminal conduct in public places. By 2016, Daley promised last month, Chicago will have one on every corner. The city has also installed red-light cameras at some 132 intersections, with another 330 planned.

So what exactly is different about those cameras? Well, they are trained on the citizenry, not on the police. What's sauce for the goose seems to be regarded as a dubious liquid substance when proposed for the gander. The city is less eager to capture video evidence if it may expose wrongdoing by its own law enforcement agents.

But the rest of us might want to keep unsleeping electronic eyes on the people with guns and badges. A city with a good police department can gain a lot from squad-car video cameras. A city with a bad one can gain even more.