Hutchins High School earlier this week unfolded in less than two minutes and began when another student let the armed suspect inside through a locked side door, Dallas ISD Police Chief Albert Martinez confirmed Thursday.

Hours after the shooting, a 17-year-old suspect turned himself in at the Lew Sterrett Justice Center in Dallas and was booked into Dallas County jail at 9:32 p.m., records show. Charges included aggravated assault/mass shooting.