Heather MacDonald of the Manhattan Institute has this op-ed, with the above headline, in the WSJ.

The recession of 2008-09 has undercut one of the most destructive social theories that came out of the 1960s: the idea that the root cause of crime lies in income inequality and social injustice. As the economy started shedding jobs in 2008, criminologists and pundits predicted that crime would shoot up, since poverty, as the "root causes" theory holds, begets criminals. Instead, the opposite happened. Over seven million lost jobs later, crime has plummeted to its lowest level since the early 1960s. The consequences of this drop for how we think about social order are significant.

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The recession crime free fall continues a trend of declining national crime rates that began in the 1990s, during a very different economy. The causes of that long-term drop are hotly disputed, but an increase in the number of people incarcerated had a large effect on crime in the last decade and continues to affect crime rates today, however much anti-incarceration activists deny it. The number of state and federal prisoners grew fivefold between 1977 and 2008, from 300,000 to 1.6 million.

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The spread of data-driven policing has also contributed to the 2000s' crime drop. At the start of the recession, the two police chiefs who confidently announced that their cities' crime rates would remain recession-proof were Los Angeles Police Chief William Bratton and New York Police Commissioner Ray Kelly. As New York Police Commissioner in the mid-1990s, Mr. Bratton pioneered the intensive use of crime data to determine policing strategies and to hold precinct commanders accountable--a process known as Compstat. Commissioner Kelly has continued Mr. Bratton's revolutionary policies, leading to New York's stunning 16-year 77% crime drop. The two police leaders were true to their word. In 2009, the city of L.A. saw a 17% drop in homicides, an 8% drop in property crimes, and a 10% drop in violent crimes. In New York, homicides fell 19%, to their lowest level since reliable records were first kept in 1963.