There was an event at school that day if I understand correctly. It was the end of the school year. If you think doors are not propped open on those days to let big groups of parents in and out I don't know what you're thinking.
But yeah, since that teacher already probably literally wants to die--if she is already not one of two teachers who died--go ahead and vilify her more. Teachers don't get enough of that crap and there are SO MANY people banging on the school doors who can't wait to be teachers!!!!!!!
Maybe a deserved prosecution will give teachers/school officials pause before willingly compromising the security of their schools.
That said current school security is a joke and unless doors/movement are controlled it will remain a joke.