[Alas Babylon!]

Update on story at source:

The explosive appeared to have been in the area more than a day, according to Lt. Mark Torre, the commanding officer of the NYPD’s Bomb Squad said. He ruled out authorities’ initial suspicion of a self-inflicted fireworks mishap.

So... Not a firework.

Then what was it?

[wally_bert]

I doubt the full truth will make it out for at least the time being.