A man in his early 20s robbed an El Cajon dry cleaning store Monday and locked the clerk in a bathroom before he escaped. Elizabeth Masters was working in the Eldorado Cleaners and Laundry in the 2900 block of Navajo Road at 6:35 p.m. when a black man entered the store, El Cajon police spokeswoman Jackie Swan said. Masters asked if he was going to rob her and he said yes, Swan recounted. The man took money from the cash register, locked Masters in the bathroom and fled on foot, Swan said. Masters was not injured. Police did not know what kind of weapon the man had. He was described as 5 feet, 5 inches tall, 120 pounds, wearing a mustache and a white sweater with a hood.