Did Ruhenheim folks actually turn on each other?

I see posts in here trying to understand how Johan manage to make inhabitants of a peaceful town turn into each other. But... I don't think that's what happened.

In the anime, we don't see any inhabitant turn their gun into another one. The only inhabitant shown shooting a gun is Herbert Knaup against Johan, 1. a foreigner, and 2. he's clearly depicted as insane and protecting and child.

I think what really happened is Roberto and his men doing the rampage and trying to fake it into a mass hysteria episode. They even try to make Wim believe he's the one who killed the 3 children by leaving him alive with his gun instead of just killing him.

Johan wanted the massacre to look like mass hysteria to erase all trace of him while committing suicide.

This made me wonder whether the 511 Kinderheim killing also really was mass hysteria and not some kind of staged operation, but there's no real element against it as Johan is shown hiding during the whole episode.