A 15-year-old boy was killed in a stabbing that started out as an attempted robbery on a CTA Red Line train on the South Side Monday, Chicago police said. An armed robbery aboard a CTA Red Line train led to the fatal stabbing of a 15-year-old boy, police said. At about 3:04 a.m. in the 200-block of West 63rd Street, police said the boy was armed with a gun and was a part of a group of seven people who were attempting to rob a person on the train, Chicago Police Chief of Detectives Brendan Deenihan said. The person they...