I have to say something, I can't shelve it any longer

A kid threatened to shoot up my school. I heard him say it, then another kid told the admin and they did nothing. Here's what happened. <br><br>A kid was misbehaving in class and clearly and loudly said "I might just shoot up this school". I was there. I heard him say it. When I heard him say it, I put the lesson on auto-pilot and walked over to this kid and tried to determine if he was being serious or just talking shit. He was serious. I could tell by his affect and tone. He was completely calm and serious. He told me he was serious. I immediately pulled the teacher over and told her what he said and she thanked me and said she'd take care of it. I went back to teaching. The next day, I asked the teacher what happened and she said the admin dropped it. <br><br>Fast forward a month, I saw the kid in the hallway and he was clearly upset. I asked him what was wrong and he told me he was upset with the admin for not doing anything about his threat. I didn't know how to respond, so I just said "huh?" He elaborated and told me the admin didn't do anything about his threat, and he thought they should have taken him seriously. I was floored. I told him to do something else when he feels that way and he laughed maniacally and told me he already did something else and he felt much better and that if I didn't hear about it in the news, then it wasn't my problem. He was also calm and serious. I didn't know how to respond, so I just walked away. <br><br>I shelve this incident because school shootings are very real and a scary topic. I know I live in one of the states that just legalized concealed carry weapons in schools, if that helps paint the picture of where I am. But I feel like I need to say something since I heard the threat, I saw the lack of response from the admin, and then I caught the kid a month later telling me that he already did something about it. What's the protocol for this? How do I report it? I've been a teacher for 20 years and I've already been told by two colleagues that this kid has a history of violence. <br><br><br>Edit: I am so grateful that you're all pushing me to do something. I am going to talk to the admin tomorrow before school and report what I heard. I'll also report it to the police. <br><br>I need to say that I give you all so much credit for the strength you have to advocate for your students. I understand now that not saying anything is perpetuating the problem.