»In which the veil lifts

It was the fenugreek! The New York Times's City Desk has the update, including the steps taken by the city's crack detectives:

On Thursday, the city announced that the mystery had been solved. The source of the odor was a plant in North Bergen, N.J., which processes seeds of the herb fenugreek to produce fragrances.

“Let me say at the top that the smell that everybody reported and has been reporting for a long time, from back, one of the earliest times was four or five years ago, has never been a health hazard,” Mayor Michael R. Bloomberg said. “In this day and age, we must take every possible threat to our safety seriously no matter how innocuous it might be.”

He added, “It wasn’t exactly akin to searching for a needle in a haystack, but a smell over a very large area.”

The city even revised its protocols to respond to such “maple syrup events” to improve response times; it analyzed winds, tides and atmospheric conditions.