It's a scene procedural writers probably see in their sleep - a burglar slides open a window, grabs the jewels, and high-tails it, leaving screaming alarm sirens in his wake. The dispatcher gets the call and picks up the radio. Cut to: an officer of the law or two, hanging out in the cruiser or posted up on a corner - and munching on doughnuts.
But every cliché was born for a reason. A cowboy needs a horse, a fireman needs a dalmatian, and a doctor needs a stethoscope. But why does a cop need a doughnut?