There will be an emergency response, and the news will inform the rest of us.
The person with the gun will either be killed or captured.
In the following days, while the families of the victims make funeral preparations, people will argue about gun laws. They'll post memes and link articles and videos that either validate or falsify the cause of bloodshed.
People will argue politics, and use the event to either validate or falsify their opinions of certain politicians and political parties.
They'll argue religion. They'll point out hypocrisies and inconsistencies, and there will be endless discussion.
The families of the victims will bury their loved ones, and we will raise them up in the spotlight and say "look at this. Look at this pain. This pain could be yours one day. That could be your loved one in the ground. It has to stop."
We'll talk about the media, and what bleeds and leads and increases ratings.
We'll talk about our culture.
We'll talk about other cultures.
We'll talk about what could have been done. How to prevent the next one. And the next. And the next after that.
And we'll point fingers, and debate, and discuss, and we'll win arguments. We'll keep reading and watching the news and taking it all as signs that the world is coming to an end, praying and hoping that we won't be next. That our loved ones won't end up on the news or in the ground.
We'll do all these things because it helps. It's how we cope with the fear of it, the spidery thrums in our guts that never really go away.
We'll do all this, and the victims will still be dead. The families will still be devastated. The killer's reasons will still be their own.
Rinse and repeat. This is our world now.