Who/What is "Concerned Citizen" in The Witcher 3?

In Novigrad I keep finding sheets of paper with messsages involving the "Eternal Fire" and Novigrad's church. They seem to be written by someone who is against Magic, Witches, Mages and anything involving the Conjunction (pretty much like the talk you usually skip when starting the game).

I remember I once found a corpse in a road and Geralt said: "It wasn't Nathaniel. S••t"

Nathaniel is Vegelbud's murderer that Geralt managed to track down and kill. Along with the corpse, another of those messages.

All of them are signed by a certain "- Concerned Citizen" and are named "Concerned Citizen Sermon" when in the Inventory. Apparently, they are even resellable!

Now, who is this guy? Does he appear in the game or he's just a kind of Easter Egg?

Solution 1:

This is part of the 'Carnal Sins' quest. The Reverend Nathaniel is not in fact the serial killer, when you find him if you just go ahead and kill him immediately you have acted to hastily and you can no longer find the real killer. When you do this you start to find these notes around Novigrad, they are telling you that the killer is still at large and you got the wrong person.