PONTIAC, Mich. — A stoic Ethan Crumbley admitted to an Oakland County judge Monday that he went on a shooting rampage in Oxford High School last year that left four of his classmates dead and seven others wounded. In what was initially to be a routine in-person pretrial hearing before Oakland County Circuit Judge Kwame Rowe, Crumbley’s attorneys Monday entered the guilty plea to 24 criminal charges including terrorism causing death and first-degree murder, which carry up to life in prison. During the hearing that commenced 21 minutes after the scheduled 8:30 a.m. start time, Crumbley, his left…