MILWAUKEE - Flames destroyed a corner grocery store near 21st and Meinecke late Friday night and police believe arson is to blame. Three firefighters were injured while fighting the blaze. One suffered a shin and shoulder injury; one injured a finger; and the last injured his back. All three were treated and released. The Mark Food Mart was destroyed and is a complete loss. Damage is estimated to be $125,000. Police are still investigating how the fire started.