Two bandits dressed as Federal Express delivery men robbed a diamond business at gunpoint Tuesday in Manhattan's Diamond District. The heist took place just before 1 pm on the sixth floor of a building in the district in midtown. No one was injured in the robbery and the thieves escaped. Investigators were still trying to determine exactly what the men stole and how much it was worth, said Detective Kevin Czartoryski, a police department spokesman. Police were hunting for the suspects and checking to see whether their faces were recorded on security cameras in the building, which is home to several businesses dealing in precious stones.