Images of students piling tables, chairs and printers against doors on social media sparked alarm and raised questions -- yet it was hardly the first time students at a university or school were unable to lock their doors during a shooting.
The same issue arose during other recent deadly attacks, including one at Virginia Tech in 2007 where students barricaded themselves inside rooms and at Sandy Hook Elementary shooting in 2012 where teachers did the same.
Yet once an active shooter is in a building, most security experts agree getting into a locked room is one of the most effective deterrents against getting injured or shot.
"How many deaths would it have taken for us to address this issue more seriously?" said Jesus Villahermosa, president of Crisis Reality Training, noting that an assailant, knowing police are on the way, usually won't bother trying to access a locked room.
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The university said yesterday it was "assessing safety measures" across the campus and will make appropriate changes. It's unknown exactly how many school and university classrooms don't have doors that can lock from the inside.
Villahermosa said the issue is more prevalent on college campuses than K-12 schools.
There are a variety of reasons why a school may not have classroom locks.
Older buildings constructed at a time when classrooms typically contained just desks and a chalkboard and not the expensive technology many have today frequently did not include them.
Others worry locking doors from the inside in itself could pose a threat. If an attacker walked inside and locked the door, students would be trapped. And the cost of installing new doors and locks can stretch into the millions.