A man was shot and killed by an acquaintance at his front door Thursday in Grand Crossing.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 the victim answered the door, Chicago police said.Lorenzo Moore suffered a gunshot wound to the chest and was taken to University of Chicago Medical Center, where he died, police and the Cook County medical examiner's office said.No arrests were reported.