Soft Target: Stephen Hunter

Black Friday America's largest shopping mall Suburban Minneapolis 3:00 P.M.
Ten thousand people jam the aisles and the escalators of America, the Mall-a giant structure with its own amusement park located in the spacious center atrium. Of those people, nine thousand nine hundred and eighty-eight have come to shop.
The other twelve have come to kill.
Stephen Hunter's hyper-drive, eighth-gear thriller chronicles the day when the unthinkable happens: terrorists descend upon the heartland, opening fire in mall corridors and executing innocent victims one by one. Those on the upper floors, including retired Marine sniper Ray Cruz, take cover or get out any way they can, but within minutes the gunmen have rounded up more than a thousand hostages, and the story comes down to one man with a gun.
Except Ray doesn't have a gun.