(IDEX Online) - A gang of nine masked thieves used hammers to smash glass display cases in a brazen attack on a jewelry store.Police have released CCTV footage of the attack on Iceberg Diamonds, at the Sun Valley Mall, in Concord, California, USA.One of the thieves, brandishing a hammer, prevented staff from intervening. The raiders fled before police arrived on Tuesday evening.Shoppers at the mall initially mistook the sound of breaking glass for gunshots.The smash and grab raid was over in under a minute. The perpetrators reportedly took almost the entire stock.Screengrab courtesy Concord Police Department