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.”