Police are investigating a violent, late-night robbery at an Iowa City grocery store.Two workers who’d just locked up the Fareway grocery store say an armed man ordered them to lie down, while a companion grabbed the store’s bank-deposit bag they were carrying. The employees say the men kicked and punched them and used racial epithets, then fled on foot with the cash. The workers say both thieves were thin, six feet tall, and wore ski masks. The two workers were treated for minor injuries.