For a blissful 36 hours beginning on Sunday night, there was no gun or knife violence reported in New York City.

Officials couldn't remember the last time that happened. But it may not be as rare in the future. Homicide rates in the Big Apple have fallen continuously since the 1990's.

This year may hit a record low annual rate of just over 400 murders, a number not seen since about 1960.

"It's an almost impossible figure, but their programs have been fabulously successful in stopping crime," Tom Reppetto, a NYPD historian, told the NY Daily News.

Murders are down 23 percent since last year, reports the newspaper, and there have been 10 percent fewer people shot.

The same drop in violent crime is being reported all over North America — in big cities too, like Los Angeles which last year recorded its lowest homicide rate in 44 years.

Also notable, the city of Newark in 2010 saw an entire calendar month go by without a single homicide. As New Jersey's largest city, it hadn't seen a similar month since 1966.

Experts can only speculate on why the crime rate continues a steep decline. Possibilities include stepped-up community policing, government programs targeted at youth, and programs aimed to reduce recidivism in newly released prison inmates.