I wonder if he has a source on the inside that tipped him off.
Or maybe the shooter is an ex cop, and thus knows procedure, and can 'think like a cop'. I think there are at least 2 involved, so maybe one is an ex cop and the other has former military/soldier. Tactical and weapon experience?
I've been wondering too\. "I am God" ties in with Mark Furman's comment and maybe the reason for the Dear Policeman wording.