"That is exactly the kind of good news in the places that need it most," Zimring said. "If I were looking for something as a mayor or police chief in Oakland...I would cast my head over my shoulder and take a look at Richmond."
Homicides in Oakland dropped to one of the lowest in years. However, the city has seen homicide rates fluctuate before. In 2010, there were 95 homicides, with that number rising until 2013.
"Oakland had been having enormous difficulties in recent years and the reduction, which was not insignificant, was really simply a continued high rate with less of a problem than it had been," Zimring said.
San Francisco's homicide rate also dropped significantly. San Francisco's District Attorney George Gascon admitted the reason is difficult to pin down.
"I think there are also other things that we don't quite understand right. There are demographic shifts. There are economic issues, there are many other factors that sometimes also contribute," Gascon said.
While San Jose's number of killings fell, this was the third consecutive year the city had more than 40 homicides. That has not happened since 1997.
So what's a city to do? Zimring recommends hiring more cops.
"While we may not know how to drive homicide rates down, we know a great deal more about effective street policing than we thought we knew 20 or 25 years ago," Zimring said. "The problem lately, in this neck of the woods, has been getting enough money to get enough police man power to put it to the good uses we know about."
Alex Emslie and Mina Kim of KQED News contributed to this report.
