I fully expect "the checklist" to be amended with "write a manifesto glorifying Trump / Conservatives / non-Communists."

Somewhere between "hand a crazy person a nice shiny new AR-15 with no wear and tear on it" and "scrub social media of this guy's footprint so avoid research after this goes down", the FBI will just write their own manifesto. They'll put out the fakeifesto so no one asks about a real manifesto. Scoop up any real documents and Raiders of the Lost Ark it away.