It was writings laid bare in a notebook found in Luigi Mangione’s possession, authorities say, that would help investigators build the federal case against him – a well-planned homicide that involved weeks of stalking the movements of his alleged victim,

Luigi Mangione, the accused killer of UnitedHealthcare CEO Brian Thompson, is expected to appear on state murder and terrorism charges in Manhattan on Monday — after being separately charged with federal death penalty-eligible offenses following his climactic return to City.