The 18-year-old suspect is scheduled to appear in court Tuesday in connection with the shooting.
The 15-year-old suspect will go to juvenile court, although an exact date for the student's appearance wasn't known, sheriff's office spokeswoman Debbie Tanna said.
Sheriff Butler said the two teens were caught with the help of surveillance video which showed them carrying the rifle inside the school. The suspects were either in the hallway with the door open or outside the breezeway where Abercrombie was walking.
While the high school has metal detectors, Butler said he didn't know if they were used on a daily basis at the school.