The school had 1 SRO to cover a 45 acre campus with more than 3000 students. The building where the shooting happened is a 3 story building.
There is no way one person could secure that school. The coach who was killed was also a security guard. He was not armed. He died shielding children with his own body.
No serious person could have claimed this school had adequate security even before the shooting.
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I think that is normal for many districts. JMO.