The shooting at Wilmer-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.

Tracy Haynes, 17, was booked into Dallas County Jail at 9:32 p.m. and is facing a charge of aggravated assault mass shooting. The arrest came after four students were injured in a school shooting Tuesday afternoon, about a year to the day when gunfire erupted on the same campus.