The former third-grade teacher, Stephanie Hale, recounted the harrowing moment during the trial of the first of two officers charged with negligence, Adrian Gonzales, who prosecutors said was the first officer to arrive at the scene and learn the whereabouts of the gunman moments before the assailant entered the school. Mr. Gonzales is facing 29 counts of abandoning and endangering children. His lawyers argued that he did the best he could with the information he was given at the time.