A “Ghostbusters” cameraman helped police track down a woman who police said pushed a 72-year-old grandmother to the ground in Chinatown, leaving her with a fatal head injury. The attack took place about 7:30 a.m. Wednesday at Essex and Chauncy streets, where a scene from the remake of the hit movie was being shot. Tajanetta Downing, 24, of 
Jamaica Plain later told officers she was crossing the street when an elderly woman bumped into her, police said.