New York City is set to roll out 400 video surveillance cameras all throughout the Big Apple.

Only 400?

Video cameras don't stop 100 percent of all crimes, obviously, but stories like this can have an impact:

PHILADELPHIA -- A woman on her way to work was shot in the back of the head by a man who followed her from a bus stop, a killing recorded by post office surveillance cameras.

Police on Wednesday released grainy images of the crime in hopes that someone will come forward with more information.

The killing of Patricia McDermott has Philadelphia shaken up like few crimes can impact a major city, and her killer is still on the loose. But the chances are good her killer will be caught and will spend the rest of his life in prison because a camera recorded his actions, and a judge and jury would be hard-pressed to show him any mercy.

MORE: Some folks think having that many video cameras might be "scary." Could that be any scarier than this?