school shoot up

This was YEARS ago and I was told not to dare talk about it by the cop.
I was in one of my classes and it nothing was happening, we had all finished our work and were just sitting and talking and using our phones. 
Well this kid that sat next to me leaned over in his seat and whispered to me "on senior day, I'm gonna blow everyone's head off. Every person I see is gonna die" 
And I was just like. 
WHAT THE FUCK. So I waited until class was over and I waited for everyone else to be in their class and I went to the principle and told him what happened. I filed a police report and the school cop straight up went off on me about how I profiled this kid, based on what he wears, what he's like. He didn't really have any friends.. other than that I don't know much about him. And then they told me to keep my mouth shut. Not to tell any other students. This kid was at school the next day and I was like??? What the fuck? I don't care what you look like. You threaten to shoot people you need to fucking go. So my mom already knew what was going on because I texted her at school while I was filing a police report. When I got home that next day I told my mom that he was STILL AT SCHOOL like Nothing happened. My mother had to go up to the school and threaten to get the news involved if they didn't do something. He ended up being expelled. My principle and the school cop gave me so much crap, got everyone together and gave speeches on bullying and stereotyping people 🙄like I'm some mean bully for TELLING SOMEONE THAT A KID HAD TOLD ME WITH HIS OWN MOUTH THAT HE WAS GONNA KILL PEOPLE. do you think I did the right thing? I think I did. I don't know how else I was supposed to act? Just wtf 🤐 
They made me feel like I didn't do the right thing. They made me feel like a jackass which confused me because they were my authority and I had always been told what to do in situations like this. There were signs in our school saying speak up about things like this. 😒 
Like come on 
Edit: that was my senior year and I did end up leaving that school and finishing on online school. I am 21 now. I was 17 when this happened.