A concealed carry holder intervened in an argument between two people and fatally shot one of them Friday afternoon in the Washington Park neighborhood.About noon, a 26-year-old man was arguing with a woman he knew near a sidewalk in the 300 block of East 56th Street, Chicago police said.The man with a concealed carry license, 23, was driving by when he saw the two arguing, according to police. He stopped his car and intervened when he saw the 26-year-old man brandish a gun, police said.The 23-year-old retrieved a gun from his car and fired shots, striking the 26-year-old in his chest, police said.The still-unidentified victim was taken to University of Chicago Medical Center, where he was pronounced dead, police said.The 23-year-old, who has a valid firearm owners ID card, remained at the scene and was taken into custody, police said.No other injuries were reported. Detectives are investigating.