Why didn’t they let medics help the massacre survivor children from Stoneman Douglas?

Why weren’t medics allowed to tend to massacre victims at Stoneman Douglas High School?

https://www.msn.com/en-us/news/us/more-medics-kept-asking-to-go-in-and-rescue-wounded-at-stoneman-douglas-they-kept-being-told-no/ar-AAy6Z0A?ocid=spartanntp