The dipshit could’ve been using services under their actual name. I sadly don’t remember which shooting it was but the shooter streamed it on Facebook live. So that’s easy for a journalist.

If you posted a deranged manifesto anonymously on 4chan or similar but mention the gruesome deed before it happens that’s a good link to your dipshit’s online history.

There is a show on German TV that is a rough copy of Last Week Tonight. Every once in a while they surprise their audience with a show that’s about the audience. You need to register for tickets with your name and email and then the researchers mercilessly dig through all the stuff people have been posting online or stuff posted about them by others. And then they gently rib them or surprise them on the show and to compensate for the public embarrassment they get a prize. It’s a concept inspired by the Snowden leaks. It’s unreal how easy it is to link people to their digital footprints. Even anonymous accounts on reddit or whatever. Armed with face recognition and syntax analysis it’s almost trivial to uncover these links. This is the sort of digging modern journalists need to do. So it is not surprising that they quickly find any dipshit’s profiles after they shot innocent people.