Mayor de Blasio called the explosion an “intentional act,’’ but

 not believed to be connected to terrorism.
 Oh, of course not.
But tensions only rose when, three hours after the blast, a second device was found four blocks away — a pressure cooker that an early investigation found was likely also a bomb.
So that's two blasts, and a third bomb, in one day.  Couple of months after someone stepped on a 'fireworks experiment' in a park. And pressure cookers, where have we heard that before...