Five days before 18-year-old Barnard College student Tessa Majors was slashed to death in Morningside Park at the edge of campus, a younger teenage girl was chased into the 118 Deli one block further away. The younger girl lost her footing as a boy who would prove to be 13 came in after her. “He kicked her on the floor,” the woman behind the counter would recall. “Situation like that, all I know is I got to call the cops. Once I see something like that, I’m calling the cops.” The counterwoman, who declined to give a reporter her name,...