A man was shot and killed by an acquaintance at his front door Thursday in Grand Crossing, according to police.The suspect arrived to the 28-year-old man’s home in the 200 block of East 69th Place and knocked on his front door about 9:50 p.m., then fired shots when he answered the door, Chicago police said.Lorenzo Moore was shot in his chest and taken to University of Chicago Medical Center, where he died, police and the Cook County medical examiner's office said.No arrests have been reported.