> But criminologists differ about the cause of the continued declines. Mr. Zimring said that while better policing accounted for much of the decline in crime since 1990, it was no longer a primary driver. New York is “tiptoeing” toward a 90 percent crime decline for reasons that remain “utterly mysterious,” he said.
The "27 straight years" caught my eye, and reminded me of something I saw a good decade ago, so may I suggest something controversial?
It doesn't perfectly match 27 years ago, but this is across the whole US, not just NYC - (popular) violent video games are highly correlated with the drop in crime: http://oi25.tinypic.com/2r6ns4y.jpg
(Correlation <> causation, but I _definitely_ think it merits more investigation... does anyone else happen to know more?)