I offer compassion and thoughts of sympathy to them, with a prayer or mantra. Over 15 years ago I worked alongside Paramedics and saw firsthand some very graphic disturbing sights, the most of which were motor vehicle crashes.
Its very difficult to get it out of your mind, but a technique I used was to envision or visualize a wall in-front of me and the graphic scene, it helped keep me detached as it were, so I wasn't so brought into it emotionally, but very hard indeed when you have alive people screaming for help incl children, you just have to keep calm and do the best you can, dealing with the trauma later when your alone, and as said its about going through one stage, one step at a time in your mind in that you did everything you could, the person has died but my religion the spirit is very much stil around, and I have seen "dead" people on and off for years which you may not believe me, they are also not demons like some religions claim but peoples souls that are still locked to the earth plain from a crash or sudden death i.e murder, they feel no pain at death, its just over but very often sudden deaths the person doesn't actually know they are dead, and they keep
hanging around sometimes causing haunting but a haunting is not like portrayed in films or tv, its nothing direct as that.
Anyway, dealing with graphic content. Unless you need to see it, dont look for it. I recollect in the early 00s when the famous beheading videos were around in Iraq of many American, and other nationalities seeing those and being disturbed by them. Some still in my mind as fragments today but I dont get affected by them, its just if they did enter the mind simply say "I am sorry please forgive me I love and thank you" as that is a strong compassion prayer not bound to any religion whatsoever, its neutral but strong at giving love to whatever, whoever you think about at the time.
Also just remember they may be dead on this physical plane but they are alive always, and very likely will be around family members at the very moment. You can if you feel so strongly, get the names of the people that died if its listed, or if you have a photo of them all when alive to concentrate on, or if better, just visualize in quiet mediation on the students in that location on that day who died, and speak out with your heart, mean it from within that you send love, do this by breathing in through the heart, and out through the heart imagine a loving color being sent out to them from you with love, compassion and support. Do that, seriously, do that they will hear you, they have not died on the spirit plane and can receive this, it will help them pass over.
Once you have done this, just move on. See a white light and go through it. Dont watch the video again. Perhaps light a candle afterwards in memory.