It doesn't matter. Authorities (at least their managers/directors) think in terms of PR/Damage Control and Risk. The fallout if they did nothing and something

It doesn't matter. Authorities (at least their managers/directors) think in terms of PR/Damage Control and Risk. The fallout if they did nothing and something happened (maybe even just reporter reporting that tweet was ignored by FBI) would be enormous. Much, much worse than fallout that occurs for "overreacting". And once they've reacted it's very hard to admit they are wrong or ever let go (as in they are unwilling to accept PR/blame). Just to avoid the .001% chance of headline "FBI had perpetrator in custody but let him go!" Sadly, the public is a ignorant, fickle, short-sided, lynch mob. Public facing organizations are(have to be) driven by risk mitigation rather than being effective.