My 14 year old brother was brutally jumped and I’m not sure how to help him get through it

I’m 21, and my 14-year-old brother was brutally attacked by four 17-year-olds. I saw the video, and it’s so disturbing I couldn’t even finish watching—it’s sickening. In the video, my brother is lying face-down on the ground while they beat him and stomp on his face. He’s completely defenseless.
Only one of them was prosecuted, and that person only received probation for assault—no jail time. I can’t get the image out of my head: my helpless baby brother, unable to fight back because he was so outnumbered. I’m disgusted and heartbroken, and I can’t begin to imagine the pain he’s going through.
Now, he doesn’t want to go back to school and is asking to switch to online learning. He already tried transferring to a different school and even moved towns, but the video somehow spread to his new school, leaving him feeling hopeless.
I’m at a loss for what to do. I can’t believe anyone could be so cruel. For context, one of these boys had bullied him all year. The attack happened when my brother went off school property to a pizza place for lunch—this group dragged him behind a building and jumped him for over an hour.
Does anyone have advice on how I can support my brother and help him move forward after this?