ST. LOUIS — A man was shot and killed Monday morning in downtown St. Louis by a gunman with whom he had fought minutes earlier, police said. Police responding to a shooting call shortly after 10 a.m. in the 700 block of North Tucker Boulevard found the man shot outside, Maj. Ryan Cousins said at the scene of the shooting. The victim was pronounced dead at the scene. Tucker was closed to traffic at Convention Plaza and Washington Avenue; the man's body was found on the sidewalk in front of The Globe Building. "Any homicide is unnerving," Cousins said, "but for this one to happen here, at this time, very much so." Witnesses of the shooting told police the man was shot by a gunman after the two fought minutes earlier down the street near a Shell gas station on Convention Plaza, Cousins said. The man was chased across the street before being shot. Police have not learned what sparked the argument.