Society for the most part is disgusted for a while with mass shootings, then they move on.
If it does not affect them personally, they don't really care. People can normalize any situation, especially when they have not directly been influenced by the situation, they can even joke about it. In mass shootings, society glorifies these killers for example by selling and buying their paintings, and making money off tours as has happened with Serial Killers, Gacy's clown pictures for instance, or Dahmer's Tours!!
These were tragedies for someone at one point in their lives, entire families were devastated but society quickly loses sight. I do not believe we can profile enough to find them 'before' rather than identify after. I have had 4 folks murder someone who were part of my office's Domestic Violence Batterers' Program. One finished my program. Two signed up, then disappeared. The fourth, signed up, and moved to another part of the country to finish. 3 killed their partners. One killed his cellmate while in prison on violence charges!! One of the ones who killed his partner, strangled his girlfriend by choking her for 4 minutes as per the coroner. He not only wanted her dead, he wanted her really really dead. BUT, when the cops arrived, he was crying because he realized he had killed his girlfriend and NOT his mother. When he finished our program in Beverly Hills, I remember saying to him, "Dude, you are 29, you have cleaned up from drugs, your music career is now looking very good. Stay sober and clean from drugs, and you should do fine. Mess up again and you could be in trouble." He was wasted off his ass when he strangled her and was devastated.
The one who strangled his cell mate, was on a major sports team. He transferred to another city. The program there called, and asked how did I deal with 'celebrity' folks. I said, "Just like the rest and often I am harder on them. They have to 'get over' themselves." He didn't.
Everyone has had some wacko thoughts, everyone, if they admit it, at some time or another has wished someone dead. But the so-called 'normal' person doesn't ACT on those feelings. Think about the teacher you couldn't stand, or the person who bullied you, or often, when a parent severely disciplines a child will say, "I wish you weren't my mother, I wish you were dead." AND let me tell you, as the person years ago who got the job of telling some of the kids in our school district when their parents had died during the day, whether it was an accident, or terminal illness, I had some answers like that. I remember Neil. I sat him down, his mom was in invalid. His dad has left the state after the accident so Neil and his mom lived together. She was in therapy one day and died. Neil was 12. When we talked, he cried and ran away out of the building. It took a few hours to find him hiding in the hillside. He cried, and said, "I killed her, I got mad at her, and told her why couldn't she be a real mom, and be able to drive and do things with me, and that I wished she was dead." Big ugh.
But real mass killers and serial killers are often hard to figure ahead of time. Terrorists too. Hind sight is 20/20 but foresight? Not so good.