Manifesto-validation is a difficult task.

Somebody could automate the generation of manifestos, and leak hundreds claiming responsibility after every shooting, arguing for a variety of different positions. Then the public would have less certainly about what shooter's political intent actually was - which could lead to less politically-motivated mass shootings?

I wonder if someone has ever successfully tricked the public into believing a manufactured manifesto was written by a perpetrator, when it was actually written by someone unrelated to the incident.