Need advice,

An incident happened at school in my child's 7th grade class. A male student was able to go to the cafeteria and get a knife using the teacher's name and go in the class with the knife and point it at two female students. He said it was a joke, but I dont think this is a joke. It is a very serious thing. I called the teacher to ask about it and express my concern, and she didn't seem that concerned and I asked if the principal was informed and what was done. She said she didn't inform the principal because he might get suspended, and basically, she gave him a chance because it's a first-time occurrence, and the kid comes from christian parents. I voiced my opinion and told her that it's not really a joke and it is actually dangerous. There are kids who have killed, and I asked what she knows about him and what he's capable, and she said he is a good kid and it was just a one-time thing.

I am still concerned, though, and I believe she was too soft with him. I dont feel like he should have been given a chance.
What would you do?