Amid empty streets and shuttered shops, crime rates in some of the biggest U.S. cities have dropped — with a few exceptions.

Car thefts and store robberies are spiking in some municipalities even as crime overall — especially violent offenses — dropped in 10 of the 20 most populated cities, more than halving in San Francisco alone. according to a Bloomberg News analysis of data from 10 major cities.

"It’s just a reflection of reduced opportunities for these kind of events,’’ said Daniel Nagin, a criminologist and professor of public policy at the H.J. Heinz School of Public Policy and Management at Carnegie Mellon University in Pittsburgh. "In the case of murders, these often occur in public places in bars and things like that. With those kinds of activities shut down there’s less social interaction.”

Car theft is one exception, at least in some places. In New York it’s surging, up 49 percent for the week ended April 12 as compared to the same period a year earlier. It's risen 53 percent over the past month and more than 63 percent year to date. Police have increased patrols in areas of the city where car thefts are common. Car theft was the only major crime to show an increase in Los Angeles, rising 11.3 percent for the 28 days ending April 11 from the previous period.

Burglaries are also on the rise in New York, up 26 percent year-to-date as compared to the same period in 2019. In the week ended April 12, they more than doubled in the southern half of Manhattan, where many stores are now unoccupied. Burglaries jumped almost 34 percent in Denver in March amid a growing number of break-ins at marijuana dispensaries. In Philadelphia, burglaries were down 6.7 percent overall, with residential break-ins falling 25 percent as more people stay home, but unoccupied businesses were hit hard, with commercial burglary rising 71 percent.

Robberies and burglaries dropped more dramatically in Los Angeles than some other major U.S. cities, perhaps because it closed non-essential businesses and told people to stay at home earlier than other cities, said Charis Kubrin, a professor of criminology at the University of California, Irvine.

'Property crimes are crimes of opportunity and with most businesses closed, there are simply fewer opportunities,' Kubrin said.

Each of the 10 major cities that provided data are showing a decline in rapes and sexual assaults, with San Francisco posting the biggest drop — more than 50 percent — as compared to the same period a year earlier. Kubrin said, however, that these numbers aren't a reliable indicator because the crime is notoriously under-reported, in part because of reluctance by victims to go to the police.

For the most part, murders are on the decline, and in cities showing a rise the numbers are low to begin with. A 25 percent increase in Austin, for example, is the result of one additional homicide, with the number rising from four to five.

"There are fewer opportunities for young people to get together,' Kubrin said. 'So there's less chance when there's alcohol involved for arguments to get out of hand and to result in assaults or homicides.'But unlike the decline in sexual assaults, the drop in homicides is a more reliable indicator, she said.'These are real drops,' Kubrin said.

Most cities are showing a decline in assaults, following the trend in other violent-crimes categories. Notably, the drop-off comes even after the release from prison of thousands of non-violent offenders. That may show that many such offenders need not have been put in jail to start with, Kubrin said.

Theft is also down across the board in the cities surveyed. But Kubrin said the drop in street crime may be followed by an increase in white-collar crime, such as price gauging and online fraud.

'Opportunities have shifted from the street to online,' she said. A slump in the stock market may also lead to the disclosure of financial schemes, as was the case following the 2009 recession, when frauds like Bernard Madoff's Ponzi scheme unraveled.

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