What are the next steps after a threat is identified?

I'm a teacher. I teach 28 classes in an elementary school. I do lock-down drills with 24 of those classes every year and it is terrifying. I've had students sob from fear through those drills. Five years ago, there was a situation in my school with a parent/student that caused me real fear. At that time, all three sets of our front school doors stayed wide open all day long. Concerns had already been shared by other teachers about this lack of security. I'm grateful that nothing happened. Shortly afterwards, the district got a lot more serious about security. Now all three banks of doors are locked during the day (and also back doors). All visitors to the school must be buzzed in. However, the frequency of people coming in and out still makes that a very vulnerable entrance point.

I'm afraid I have low confidence in the security of my school, but I wouldn't begin to know how to fix that.


[Edited to add: I found your second post which gives the answer to my initial question. Thank you. That some "swim back" means the situation described above is not really over. I'm not sure any resources would be able to solve the very deep issues that likely still exist for that student/parent.]