A good Samaritan trying to drive a gunshot victim to a hospital accidentally plowed into three teen-agers, killing one and injuring the others, Chicago authorities said. Marvin Ferguson, 33, was cited for driving too fast for conditions and striking a pedestrian. “He tried to do the right thing,” police officer Mike Hughes said. “He’s a victim of circumstances.” Larry White, 16, was killed and his companions, Tanice Thorpe, 17, and Tanya Porter, 16, were hospitalized in critical and serious condition, respectively. The gunshot victim, identified as Del Marie Harris, 28, was treated for a face wound and released. Ferguson was scheduled to appear in traffic court July 18.