What is considered a safe work environment? Can anything be done for witnessing an after hours ult?

I am a school teacher who works in a very bad part of town. Within the past two months I have witnessed a custodian being held up at gunpoint for his wallet and a person who stabbed another fleeing from the scene. I called 911 both times. Both of these incidents occured on school grounds, but after hours (about 7 pm). We are allowed to access the school 24 hours a day, as per district policy. Can I demand a change of school placement? Am I entitled to anything?