Hard to tell if the person knocking on the door is a threat or not. It was a TRAGIC and TERRIFYING situation for both students and teachers :( :( :(
The teacher should protect the kids already inside the class room because it's better to trust the known rather than the unknown.
My FC is 4957-4763-9094 (Pokemon Sun) PS3: hellfighter45 D3:UE, Xenoverse 1
PSN: hellfighter44 God Eater R (VITA), DB Xenoverse 2 (PS4), Rocket League